Fix #10891 - Formatting does not respect indentation within Razor comment blocks (#10893)

Altered `HtmlFormattingPassBase` to discard any `TextChange`s that start
within a `RazorCommentBlockSyntax` and added a test to catch any
regressions in the future.

Fixes #10891

Author: phil-allen-msft

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/Passes/HtmlFormattingPassBase.cs

@@ -30,7 +30,9 @@ public virtual async Task<ImmutableArray<TextChange>> ExecuteAsync(FormattingCon
 
         if (changes.Length > 0)
         {
-            changedText = originalText.WithChanges(changes);
+            var filteredChanges = FilterIncomingChanges(changedContext, changes);
+
+            changedText = originalText.WithChanges(filteredChanges);
             // Create a new formatting context for the changed razor document.
             changedContext = await context.WithTextAsync(changedText).ConfigureAwait(false);
 
@@ -48,6 +50,27 @@ public virtual async Task<ImmutableArray<TextChange>> ExecuteAsync(FormattingCon
         return changedText.GetTextChangesArray(originalText);
     }
 
+    private static ImmutableArray<TextChange> FilterIncomingChanges(FormattingContext context, ImmutableArray<TextChange> changes)
+    {
+        var syntaxTree = context.CodeDocument.GetSyntaxTree();
+
+        using var changesToKeep = new PooledArrayBuilder<TextChange>(capacity: changes.Length);
+
+        foreach (var change in changes)
+        {
+            // Don't keep changes that start inside of a razor comment block.
+            var comment = syntaxTree.Root.FindInnermostNode(change.Span.Start)?.FirstAncestorOrSelf<RazorCommentBlockSyntax>();
+            if (comment is not null)
+            {
+                continue;
+            }
+
+            changesToKeep.Add(change);
+        }
+
+        return changesToKeep.DrainToImmutable();
+    }
+
     private static ImmutableArray<TextChange> AdjustRazorIndentation(FormattingContext context)
     {
         // Assume HTML formatter has already run at this point and HTML is relatively indented correctly.

src/Razor/test/Microsoft.AspNetCore.Razor.LanguageServer.Test/Formatting_NetFx/RazorFormattingTest.cs

@@ -705,6 +705,31 @@ await RunFormattingTestAsync(
             fileKind: FileKinds.Legacy);
     }
 
+    [Fact]
+    public async Task MultiLineComment_WithinHtml ()
+    {
+        await RunFormattingTestAsync(
+            input: """
+                    <div>
+                    @* <div>
+                    This comment's opening at-star will be aligned, and the
+                    indentation of the rest of its lines will be preserved.
+                            </div>
+                        *@
+                    </div>
+                    """,
+            expected: """
+                    <div>
+                        @* <div>
+                    This comment's opening at-star will be aligned, and the
+                    indentation of the rest of its lines will be preserved.
+                            </div>
+                        *@
+                    </div>
+                    """,
+            fileKind: FileKinds.Legacy);
+    }
+
     // Regression prevention tests:
     [Fact]
     public async Task Using()