Annotate ConfiguredCancelableAsyncEnumerable T with allows ref struct…

… and update extensions

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/ConfiguredCancelableAsyncEnumerable.cs

@@ -10,6 +10,9 @@ namespace System.Runtime.CompilerServices
     /// <summary>Provides an awaitable async enumerable that enables cancelable iteration and configured awaits.</summary>
     [StructLayout(LayoutKind.Auto)]
     public readonly struct ConfiguredCancelableAsyncEnumerable<T>
+#if NET9_0_OR_GREATER
+        where T : allows ref struct
+#endif
     {
         private readonly IAsyncEnumerable<T> _enumerable;
         private readonly CancellationToken _cancellationToken;

src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/TaskAsyncEnumerableExtensions.cs

@@ -22,16 +22,22 @@ public static ConfiguredAsyncDisposable ConfigureAwait(this IAsyncDisposable sou
         /// <param name="continueOnCapturedContext"><see langword="true" /> to capture and marshal back to the current context; otherwise, <see langword="false" />.</param>
         /// <returns>The configured enumerable.</returns>
         public static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(
-            this IAsyncEnumerable<T> source, bool continueOnCapturedContext) =>
-            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext, cancellationToken: default);
+            this IAsyncEnumerable<T> source, bool continueOnCapturedContext)
+#if NET9_0_OR_GREATER
+            where T : allows ref struct
+#endif
+            => new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext, cancellationToken: default);
 
         /// <summary>Sets the <see cref="CancellationToken"/> to be passed to <see cref="IAsyncEnumerable{T}.GetAsyncEnumerator(CancellationToken)"/> when iterating.</summary>
         /// <typeparam name="T">The type of the objects being iterated.</typeparam>
         /// <param name="source">The source enumerable being iterated.</param>
         /// <param name="cancellationToken">The <see cref="CancellationToken"/> to use.</param>
         /// <returns>The configured enumerable.</returns>
         public static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(
-            this IAsyncEnumerable<T> source, CancellationToken cancellationToken) =>
-            new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext: true, cancellationToken);
+            this IAsyncEnumerable<T> source, CancellationToken cancellationToken)
+#if NET9_0_OR_GREATER
+            where T : allows ref struct
+#endif
+            => new ConfiguredCancelableAsyncEnumerable<T>(source, continueOnCapturedContext: true, cancellationToken);
     }
 }