[l10n] Use Arcade to generate resource properties (#5270)

Context: 0342fe5

Now that `Xamarin.Android.Build.Tasks.csproj` is a short-form project
(03743f3), add a dependency on the [`Microsoft.DotNet.Arcade.Sdk`][0]
NuGet package, and switch to using the
[`$(GenerateResxSource)` mechanism][1] instead of using
`%(EmbeddedResource.Generator)`=`ResXFileCodeGenerator`, which only
updates `Resources.Designer.cs` when using the Visual Studio IDEs.

For this initial use of `Microsoft.DotNet.Arcade.Sdk`, import only
`..\tools\BuildTasks.props` and `..\tools\GenerateResxSource.targets`.
Avoid importing the full `Sdk.props` and `Sdk.targets` for now because
those files have other consequences that aren't desired at this time.
For example, `Sdk.props` indirectly imports `ProjectDefaults.props`,
which sets `$(DebugType)`=`embedded` by default, and
`[assembly:AssemblyVersion("42.42.42.42")]` is added.

An advantage of `$(GenerateResxSource)`=True compared to
`ResXFileCodeGenerator` is that contributors no longer need to worry
about updating `Resources.Designer.cs` when updating `Resources.resx`.
This is especially helpful for contributors who use an editor other
than Visual Studio (macOS & Windows), because it means they no longer
need to hand-edit the `Resource.Designer.cs` file to match the format
that `ResXFileCodeGenerator` generates on Windows.

The generated file
`obj/$(Configuration)/Xamarin.Android.Tasks.Properties.Resources.cs`
has essentially the same setup as the previous `Resources.Designer.cs`.
The properties are still `internal` and still include `<summary/>`
comments to surface the non-localized messages in IntelliSense, and the
file is still updated by a design-time build any time the `.resx`
file changes.

One difference is that the new generated `.cs` file is not shown in the
Solution Explorer because it's located in `obj/`.  If any contributors
were previously using `Resources.Designer.cs` as a starting place to do
"find all references" on the property names, they would now need to open
the generated file from the `obj/` directory instead.

[0]: https://github.com/dotnet/arcade/tree/0940dc72b8d9886c1605c38f7190b984463903c6/src/Microsoft.DotNet.Arcade.Sdk
[1]: https://github.com/dotnet/arcade/blob/c6f24c0d1264f6f80ceb39d2b0477d054c3f8ffc/Documentation/ArcadeSdk.md#generateresxsource-bool

Documentation/workflow/Localization.md

@@ -11,12 +11,14 @@ so when adding a new message, follow these steps:
     ![Managed Resources Editor with XA0000 as the name for a
     resource][resources-editor]
 
-    Be sure to use Visual Studio or Visual Studio for Mac to edit the `.resx`
-    file so that the `ResXFileCodeGenerator` tool will run and update the
-    corresponding `Resources.Designer.cs` file.
+ 2. If using Visual Studio or Visual Studio for Mac, skip to the next step.
 
- 2. Use the generated property from `Resources.Designer.cs` in the
-    `LogCodedError()` and `LogCodedWarning()` calls:
+    If using an editor that does not automatically run design-time builds for
+    MSBuild targets specified via `%(Generator)` MSBuild item metadata,
+    explicitly build the project to update the generated properties.
+
+ 3. Use the generated C# property for the resource in the `LogCodedError()` and
+    `LogCodedWarning()` calls:
 
     ```csharp
     Log.LogCodedError ("XA0000", Properties.Resources.XA0000);
@@ -30,13 +32,13 @@ so when adding a new message, follow these steps:
     <AndroidError Code="XA0000" ResourceName="XA0000" />
     ```
 
- 3. After adding the new message, build `Xamarin.Android.Build.Tasks.csproj`
+ 4. After adding the new message, build `Xamarin.Android.Build.Tasks.csproj`
     locally.  This will run the targets from [dotnet/xliff-tasks][xliff-tasks]
     to update the `.xlf` [XLIFF][xliff] localization files with the latest
     changes from the `.resx` file.
 
- 4. Include the changes to the`.resx` file as well as the generated changes to
-    the `Resources.Designer.cs` file and the `.xlf` files in the commit.
+ 5. Include the changes to the`.resx` file as well as the generated changes to
+    the `.xlf` files in the commit.
 
 ## Guidelines
 

global.json

@@ -1,6 +1,7 @@
 {
     "msbuild-sdks": {
         "Microsoft.Build.NoTargets": "2.0.1",
+        "Microsoft.DotNet.Arcade.Sdk": "6.0.0-beta.20555.6",
         "Microsoft.DotNet.Build.Tasks.SharedFramework.Sdk": "5.0.0-beta.20120.1"
     }
 }