Added internal notes with link to the WinUI issue

Author: Sergio0694

Microsoft.Toolkit/Extensions/StringExtensions.cs

@@ -147,7 +147,16 @@ public static string FixHtml(this string html)
         /// <param name="args">The object which will receive the linked String.</param>
         /// <returns>Truncated string.</returns>
         [Obsolete("This method will be removed in a future version of the Toolkit. Use the native C# string interpolation syntax instead, see: https://docs.microsoft.com/dotnet/csharp/language-reference/tokens/interpolated")]
-        public static string AsFormat(this string format, params object[] args) => string.Format(format, args);
+        public static string AsFormat(this string format, params object[] args)
+        {
+            // Note: this extension was originally added to help developers using {x:Bind} in XAML, but
+            // due to a known limitation in the UWP/WinUI XAML compiler, using either this method or the
+            // standard string.Format method from the BCL directly doesn't always work. Since this method
+            // doesn't actually provide any benefit over the built-in one, it has been marked as obsolete.
+            // For more details, see the WinUI issue on the XAML compiler limitation here:
+            // https://github.com/microsoft/microsoft-ui-xaml/issues/2654.
+            return string.Format(format, args);
+        }
 
         /// <summary>
         /// Truncates a string to the specified length.