Make sure that *.* always means all files in FileMatcher (#6235)

### Context

#6151 introduced a regression where `FileMatcher` takes the pattern `*.*` too literally and returns only files that have a dot in the name. `*.*` should be special cased to mean all files in the directory, with or without an extension.

### Changes Made

Fixed the regression by explicitly testing for `*.*` and added test coverage.

### Testing

Existing and modified unit tests, repro project from dotnet/sdk#16185 (comment).

### Notes

Testing for both `*` and `*.*` is already happening elsewhere in the class. MSBuild calls `Directory.EnumerateFileSystemEntries` which under the covers uses `MatchType.Win32` and causes this behavior of unifying `*.*` with `*` on all platforms.

src/Shared/FileMatcher.cs

@@ -131,7 +131,7 @@ internal FileMatcher(IFileSystem fileSystem, GetFileSystemEntries getFileSystemE
                                     "*",
                                     directory,
                                     false));
-                        IEnumerable<string> filteredEntriesForPath = (pattern != null && pattern != "*")
+                        IEnumerable<string> filteredEntriesForPath = (pattern != null && pattern != "*" && pattern != "*.*")
                             ? allEntriesForPath.Where(o => IsMatch(Path.GetFileName(o), pattern))
                             : allEntriesForPath;
                         return stripProjectDirectory

src/Shared/UnitTests/FileMatcher_Tests.cs

@@ -5,6 +5,7 @@
 using Shouldly;
 using System;
 using System.Collections.Generic;
+using System.Collections.Concurrent;
 using System.IO;
 using System.Linq;
 using System.Text.RegularExpressions;
@@ -77,9 +78,9 @@ public void GetFilesComplexGlobbingMatching(GetFilesComplexGlobbingMatchingInfo
                 File.WriteAllBytes(fullPath, new byte[1]);
             }
 
-            void Verify(string include, string[] excludes, bool shouldHaveNoMatches = false, string customMessage = null)
+            void VerifyImpl(FileMatcher fileMatcher, string include, string[] excludes, bool shouldHaveNoMatches = false, string customMessage = null)
             {
-                string[] matchedFiles = FileMatcher.Default.GetFiles(testFolder.Path, include, excludes?.ToList());
+                string[] matchedFiles = fileMatcher.GetFiles(testFolder.Path, include, excludes?.ToList());
 
                 if (shouldHaveNoMatches)
                 {
@@ -99,6 +100,18 @@ void Verify(string include, string[] excludes, bool shouldHaveNoMatches = false,
                 }
             }
 
+            var fileMatcherWithCache = new FileMatcher(FileSystems.Default, new ConcurrentDictionary<string, IReadOnlyList<string>>());
+
+            void Verify(string include, string[] excludes, bool shouldHaveNoMatches = false, string customMessage = null)
+            {
+                // Verify using the default non-caching FileMatcher.
+                VerifyImpl(FileMatcher.Default, include, excludes, shouldHaveNoMatches, customMessage);
+
+                // Verify using a caching FileMatcher and do it twice to exercise the cache.
+                VerifyImpl(fileMatcherWithCache, include, excludes, shouldHaveNoMatches, customMessage);
+                VerifyImpl(fileMatcherWithCache, include, excludes, shouldHaveNoMatches, customMessage);
+            }
+
             // Normal matching
             Verify(info.Include, info.Excludes);
 
@@ -153,7 +166,7 @@ public class GetFilesComplexGlobbingMatchingInfo
                 @"subdirectory\subdirectory.cs",
                 @"build\baz\foo.cs",
                 @"readme.txt",
-                @"licence.md"
+                @"licence"
             };
 
             /// <summary>
@@ -355,7 +368,7 @@ public static IEnumerable<object[]> GetTestData()
                         ExpectedMatches = new[]
                         {
                             @"readme.txt",
-                            @"licence.md"
+                            @"licence"
                         }
                     }
                 };