ObjectStorage enhancements (#4102)

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## Fixes #3903 
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<!-- Add a brief overview here of the feature/bug & fix. -->

## PR Type
What kind of change does this PR introduce?
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<!-- - Bugfix -->
- Feature
<!-- - Code style update (formatting) -->
<!-- - Refactoring (no functional changes, no api changes) -->
<!-- - Build or CI related changes -->
<!-- - Documentation content changes -->
<!-- - Sample app changes -->
<!-- - Other... Please describe: -->

## What is the current behavior?
<!-- Please describe the current behavior that you are modifying, or link to a relevant issue. -->
The ObjectStorage helper interfaces and implementations currently live in the `*.Uwp` package. This means that they are not consumable from NetStandard projects, such as the `CommunityToolkit.Graph` package.

In addition, the `IObjectStorageHelper` is a mixture of support for both dictionary style settings storage, with some file storage features as well. Currently, supporting both file and folder scenarios is odd/difficult for storage endpoints that don't operate in a similar manner to `Windows.Storage.ApplicationData`.

Lastly, the support for file storage in `IObjectStorageHelper` is not complete and missing some basic CRUD operations that can make it difficult to work with in real-world application scenarios.

## What is the new behavior?
<!-- Describe how was this issue resolved or changed? -->
I've done a few things:

1. Deprecated the existing structures in the `Microsoft.Toolkit.Uwp/Helpers/ObjectStorage` folder:
    - `BaseObjectStorageHelper`
    - `IObjectSerializer`
    - `IObjectStorageHelper`
    - `LocalObjectStorageHelper`
    - `SystemSerializer`

2. Migrated some of the previous structures up into the `Microsoft.Toolkit/Helpers/ObjectStorage` folder so that they are consumable from NetStandard:
    - `IObjectSerializer`
    - `SystemSerializer`

3. Created new interfaces to replace the functionality defined in the now defunct `IObjectStorageHelper`:
    - `ISettingsStorageHelper` - Interop with values as key/value pairs, like a dictionary.
    - `IFileStorageHelper` - Interop with a file system to store values in files and folders.

4. Replaced the functionality provided by `BaseObjectStorageHelper` and `LocalObjectStorageHelper` with an implementation of `ISettingsStorageHelper` and `IFileStorageHelper`:
    - `ApplicationDataStorageHelper` - Interop with local settings and files through `Windows.Storage.ApplicationData`.

Use it like so:
```
ApplicationDataStorageHelper appDataStorageHelper = ApplicationDataStorageHelper.GetCurrent(new Toolkit.Helpers.SystemSerializer());

// Save and Read simple objects
string keySimpleObject = "simple";
appDataStorageHelper.Save(keySimpleObject, 42);
appDataStorageHelper.TryRead<string>(keySimpleObject, out string result);

// Save and Read complex objects
string complexObjectKey = "complexObject";
await appDataStorageHelper.SaveFileAsync(complexObjectKey, new MyComplexObject());
var complexObject = await appDataStorageHelper.ReadFileAsync<MyComplexObject>(complexObjectKey);

// Complex object example
public class MyComplexObject
{
    public string MyContent { get; set; }
    public List<string> MyContents { get; set; }
    public List<MyComplexObject> MyObjects { get; set; }
}
```

Altogether, this provides a transition path from the previous ObjectStorage constructs to a more granular set of interfaces with identical signatures plus enhanced support for file and folder CRUD operations.

## PR Checklist

Please check if your PR fulfills the following requirements:

- [x] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [x] Sample in sample app has been added / updated (for bug fixes / features)
    - [x] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [x] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [x] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [x] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [x] Contains **NO** breaking changes

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     Please note that breaking changes are likely to be rejected within minor release cycles or held until major versions. -->


## Other information
Looking for feedback!

Microsoft.Toolkit.Uwp.SampleApp/Controls/SampleAppMarkdownRenderer.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Microsoft.Toolkit.Helpers;
 using Microsoft.Toolkit.Parsers.Markdown;
 using Microsoft.Toolkit.Parsers.Markdown.Blocks;
 using Microsoft.Toolkit.Parsers.Markdown.Inlines;
@@ -407,19 +408,19 @@ public string DesiredLang
         {
             get
             {
-                return storage.Read<string>(DesiredLangKey);
+                return settingsStorage.Read<string>(DesiredLangKey);
             }
 
             set
             {
-                storage.Save(DesiredLangKey, value);
+                settingsStorage.Save(DesiredLangKey, value);
             }
         }
 
         /// <summary>
-        /// The Local Storage Helper.
+        /// The local app data storage helper for storing settings.
         /// </summary>
-        private LocalObjectStorageHelper storage = new LocalObjectStorageHelper(new SystemSerializer());
+        private readonly ApplicationDataStorageHelper settingsStorage = ApplicationDataStorageHelper.GetCurrent();
 
         /// <summary>
         /// DocFX note types and styling info, keyed by identifier.

Microsoft.Toolkit.Uwp.SampleApp/Models/Sample.cs

@@ -20,6 +20,7 @@
 // TODO Reintroduce graph controls
 // using Microsoft.Toolkit.Graph.Converters;
 // using Microsoft.Toolkit.Graph.Providers;
+using Microsoft.Toolkit.Helpers;
 using Microsoft.Toolkit.Uwp.Helpers;
 using Microsoft.Toolkit.Uwp.Input.GazeInteraction;
 using Microsoft.Toolkit.Uwp.SampleApp.Models;
@@ -45,7 +46,7 @@ public class Sample
 
         public static async void EnsureCacheLatest()
         {
-            var settingsStorage = new LocalObjectStorageHelper(new SystemSerializer());
+            var settingsStorage = ApplicationDataStorageHelper.GetCurrent();
 
             var onlineDocsSHA = await GetDocsSHA();
             var cacheSHA = settingsStorage.Read<string>(_cacheSHAKey);

Microsoft.Toolkit.Uwp.SampleApp/Models/Samples.cs

@@ -9,6 +9,7 @@
 using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.Toolkit.Helpers;
 using Microsoft.Toolkit.Uwp.Helpers;
 
 namespace Microsoft.Toolkit.Uwp.SampleApp
@@ -21,7 +22,7 @@ public static class Samples
         private static SemaphoreSlim _semaphore = new SemaphoreSlim(1);
 
         private static LinkedList<Sample> _recentSamples;
-        private static LocalObjectStorageHelper _localObjectStorageHelper = new LocalObjectStorageHelper(new SystemSerializer());
+        private static ApplicationDataStorageHelper _settingsStorage = ApplicationDataStorageHelper.GetCurrent();
 
         public static async Task<SampleCategory> GetCategoryBySample(Sample sample)
         {
@@ -98,7 +99,7 @@ public static async Task<LinkedList<Sample>> GetRecentSamples()
             if (_recentSamples == null)
             {
                 _recentSamples = new LinkedList<Sample>();
-                var savedSamples = _localObjectStorageHelper.Read<string>(_recentSamplesStorageKey);
+                var savedSamples = _settingsStorage.Read<string>(_recentSamplesStorageKey);
 
                 if (savedSamples != null)
                 {
@@ -144,7 +145,7 @@ private static void SaveRecentSamples()
             }
 
             var str = string.Join(";", _recentSamples.Take(10).Select(s => s.Name).ToArray());
-            _localObjectStorageHelper.Save<string>(_recentSamplesStorageKey, str);
+            _settingsStorage.Save<string>(_recentSamplesStorageKey, str);
         }
     }
 }

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/Object Storage/ObjectStorageCode.bind

@@ -1,25 +1,24 @@
-var localObjectStorageHelper = new LocalObjectStorageHelper();
-var roamingObjectStorageHelper = new RoamingObjectStorageHelper();
+ApplicationDataStorageHelper appDataStorageHelper = ApplicationDataStorageHelper.GetCurrent(new Toolkit.Helpers.SystemSerializer());
 
 // Read and Save with simple objects
 string keySimpleObject = "simple";
-string result = localObjectStorageHelper.Read<string>(keySimpleObject);
-localObjectStorageHelper.Save(keySimpleObject, 47);
+string result = appDataStorageHelper.Read<string>(keySimpleObject);
+appDataStorageHelper.Save(keySimpleObject, 47);
 
 // Read and Save with complex/large objects
-string keyLargeObject = "large";
-var result = localObjectStorageHelper.ReadFileAsync<MyLargeObject>(keyLargeObject);
+string complexObjectKey = "complexObject";
+var complexObject = await appDataStorageHelper.ReadFileAsync<MyLargeObject>(complexObjectKey);
 
-var o = new MyLargeObject
+var myComplexObject = new MyComplexObject()
 {
     ...
 };
-localObjectStorageHelper.SaveFileAsync(keySimpleObject, o);
+await appDataStorageHelper.SaveFileAsync(complexObjectKey, myComplexObject);
 
 // Complex object
-public class MyLargeObject
+public class MyComplexObject
 {
     public string MyContent { get; set; }
     public List<string> MyContents { get; set; }
-    public List<MyLargeObject> MyObjects { get; set; }
+    public List<MyComplexObject> MyObjects { get; set; }
 }

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/Object Storage/ObjectStoragePage.xaml.cs

@@ -2,14 +2,15 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using Microsoft.Toolkit.Helpers;
 using Microsoft.Toolkit.Uwp.Helpers;
 using Windows.UI.Xaml;
 
 namespace Microsoft.Toolkit.Uwp.SampleApp.SamplePages
 {
     public sealed partial class ObjectStoragePage
     {
-        private readonly IObjectStorageHelper localStorageHelper = new LocalObjectStorageHelper(new SystemSerializer());
+        private readonly ApplicationDataStorageHelper _settingsStorage = ApplicationDataStorageHelper.GetCurrent();
 
         public ObjectStoragePage()
         {
@@ -24,9 +25,9 @@ private void ReadButton_Click(object sender, RoutedEventArgs e)
             }
 
             // Read from local storage
-            if (localStorageHelper.KeyExists(KeyTextBox.Text))
+            if (_settingsStorage.KeyExists(KeyTextBox.Text))
             {
-                ContentTextBox.Text = localStorageHelper.Read<string>(KeyTextBox.Text);
+                ContentTextBox.Text = _settingsStorage.Read<string>(KeyTextBox.Text);
             }
         }
 
@@ -43,7 +44,7 @@ private void SaveButton_Click(object sender, RoutedEventArgs e)
             }
 
             // Save into local storage
-            localStorageHelper.Save(KeyTextBox.Text, ContentTextBox.Text);
+            _settingsStorage.Save(KeyTextBox.Text, ContentTextBox.Text);
         }
     }
 }

Microsoft.Toolkit.Uwp/Helpers/ObjectStorage/ApplicationDataStorageHelper.CacheFolder.cs

@@ -0,0 +1,77 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Microsoft.Toolkit.Helpers;
+using Windows.Storage;
+
+namespace Microsoft.Toolkit.Uwp.Helpers
+{
+    /// <summary>
+    /// An extension of ApplicationDataStorageHelper with additional features for interop with the LocalCacheFolder.
+    /// </summary>
+    public partial class ApplicationDataStorageHelper
+    {
+        /// <summary>
+        ///  Gets the local cache folder.
+        /// </summary>
+        public StorageFolder CacheFolder => AppData.LocalCacheFolder;
+
+        /// <summary>
+        /// Retrieves an object from a file in the LocalCacheFolder.
+        /// </summary>
+        /// <typeparam name="T">Type of object retrieved.</typeparam>
+        /// <param name="filePath">Path to the file that contains the object.</param>
+        /// <param name="default">Default value of the object.</param>
+        /// <returns>Waiting task until completion with the object in the file.</returns>
+        public Task<T> ReadCacheFileAsync<T>(string filePath, T @default = default)
+        {
+            return ReadFileAsync<T>(CacheFolder, filePath, @default);
+        }
+
+        /// <summary>
+        /// Retrieves the listings for a folder and the item types in the LocalCacheFolder.
+        /// </summary>
+        /// <param name="folderPath">The path to the target folder.</param>
+        /// <returns>A list of file types and names in the target folder.</returns>
+        public Task<IEnumerable<(DirectoryItemType ItemType, string Name)>> ReadCacheFolderAsync(string folderPath)
+        {
+            return ReadFolderAsync(CacheFolder, folderPath);
+        }
+
+        /// <summary>
+        /// Saves an object inside a file in the LocalCacheFolder.
+        /// </summary>
+        /// <typeparam name="T">Type of object saved.</typeparam>
+        /// <param name="filePath">Path to the file that will contain the object.</param>
+        /// <param name="value">Object to save.</param>
+        /// <returns>Waiting task until completion.</returns>
+        public Task CreateCacheFileAsync<T>(string filePath, T value)
+        {
+            return SaveFileAsync<T>(CacheFolder, filePath, value);
+        }
+
+        /// <summary>
+        /// Ensure a folder exists at the folder path specified in the LocalCacheFolder.
+        /// </summary>
+        /// <param name="folderPath">The path and name of the target folder.</param>
+        /// <returns>Waiting task until completion.</returns>
+        public Task CreateCacheFolderAsync(string folderPath)
+        {
+            return CreateFolderAsync(CacheFolder, folderPath);
+        }
+
+        /// <summary>
+        /// Deletes a file or folder item in the LocalCacheFolder.
+        /// </summary>
+        /// <param name="itemPath">The path to the item for deletion.</param>
+        /// <returns>Waiting task until completion.</returns>
+        public Task DeleteCacheItemAsync(string itemPath)
+        {
+            return DeleteItemAsync(CacheFolder, itemPath);
+        }
+    }
+}