Convert menus to use OverlayPortal (#130534)

## Description

This converts the `MenuAnchor` class to use `OverlayPortal` instead of directly using the overlay.

## Related Issues
 - Fixes #124830

## Tests
 - No tests yet (hence it is a draft)

Author: gspencergoog

examples/api/lib/material/menu_anchor/menu_anchor.2.dart

@@ -6,11 +6,12 @@ import 'package:flutter/material.dart';
 
 /// Flutter code sample for [MenuAnchor].
 
-// This is the type used by the menu below.
-enum SampleItem { itemOne, itemTwo, itemThree }
 
 void main() => runApp(const MenuAnchorApp());
 
+// This is the type used by the menu below.
+enum SampleItem { itemOne, itemTwo, itemThree }
+
 class MenuAnchorApp extends StatelessWidget {
   const MenuAnchorApp({super.key});
 
@@ -36,7 +37,10 @@ class _MenuAnchorExampleState extends State<MenuAnchorExample> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('MenuAnchorButton')),
+      appBar: AppBar(
+        title: const Text('MenuAnchorButton'),
+        backgroundColor: Theme.of(context).primaryColorLight,
+      ),
       body: Center(
         child: MenuAnchor(
           builder:

examples/api/test/material/menu_anchor/menu_anchor.1_test.dart

@@ -51,7 +51,18 @@ void main() {
 
     expect(find.text('Background Color'), findsOneWidget);
 
+    // Focusing the background color item with the keyboard caused the submenu
+    // to open. Tapping it should cause it to close.
     await tester.tap(find.text('Background Color'));
+    await tester.pump();
+    await tester.pumpAndSettle();
+
+    expect(find.text(example.MenuEntry.colorRed.label), findsNothing);
+    expect(find.text(example.MenuEntry.colorGreen.label), findsNothing);
+    expect(find.text(example.MenuEntry.colorBlue.label), findsNothing);
+
+    await tester.tap(find.text('Background Color'));
+    await tester.pump();
     await tester.pumpAndSettle();
 
     expect(find.text(example.MenuEntry.colorRed.label), findsOneWidget);