Simplify string comparison and move comments inline in CompletionContextHelper

Co-authored-by: davidwengier <754264+davidwengier@users.noreply.github.com>

Author: Copilot

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/BlazorDataAttributeCompletionItemProvider.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Collections.Immutable;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
@@ -63,7 +64,7 @@ public ImmutableArray<RazorCompletionItem> GetCompletionItems(RazorCompletionCon
         }
 
         // Don't provide completions if the user is typing a directive attribute (starts with @)
-        if (selectedAttributeName?.StartsWith("@", System.StringComparison.Ordinal) == true)
+        if (selectedAttributeName?.StartsWith('@') == true)
         {
             return [];
         }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Completion/CompletionContextHelper.cs

@@ -13,17 +13,15 @@ internal static class CompletionContextHelper
     /// </summary>
     /// <param name="owner">The original syntax node owner.</param>
     /// <returns>The adjusted owner node.</returns>
-    /// <remarks>
-    /// This method is trying to find the nearest Start or End tag. Most of the time, that's a level up, but if the index the user is typing at
-    /// is a token of a start or end tag directly, we already have the node we want.
-    /// Invoking completion in an empty file will give us RazorDocumentSyntax which always has null parent.
-    /// Either the parent is a context we can handle, or it's not and we shouldn't show completions.
-    /// </remarks>
     public static RazorSyntaxNode? AdjustSyntaxNodeForCompletion(RazorSyntaxNode? owner)
         => owner switch
         {
+            // This provider is trying to find the nearest Start or End tag. Most of the time, that's a level up, but if the index the user is typing at
+            // is a token of a start or end tag directly, we already have the node we want.
             MarkupStartTagSyntax or MarkupEndTagSyntax or MarkupTagHelperStartTagSyntax or MarkupTagHelperEndTagSyntax or MarkupTagHelperAttributeSyntax => owner,
+            // Invoking completion in an empty file will give us RazorDocumentSyntax which always has null parent
             RazorDocumentSyntax => owner,
+            // Either the parent is a context we can handle, or it's not and we shouldn't show completions.
             _ => owner?.Parent
         };