Adjust defaults in docs to match new defaults in code. (#34664)

(and fix grammar)

See: https://github.com/flutter/flutter/pull/21826

packages/flutter/lib/src/rendering/layer.dart

@@ -983,7 +983,7 @@ class ClipRectLayer extends ContainerLayer {
   }
 
   /// {@template flutter.clipper.clipBehavior}
-  /// Controls how to clip (default to [Clip.antiAlias]).
+  /// Controls how to clip (defaults to [Clip.hardEdge]).
   ///
   /// [Clip.none] is not allowed here.
   /// {@endtemplate}