Widgets app refactor (#22269)

* Refactor of cupertino/material/widgets app

* update docs 

* Update tests for const
diff --git a/dev/manual_tests/lib/animated_icons.dart b/dev/manual_tests/lib/animated_icons.dart
index 718dba8..3cf6f10 100644
--- a/dev/manual_tests/lib/animated_icons.dart
+++ b/dev/manual_tests/lib/animated_icons.dart
@@ -7,9 +7,9 @@
 class AnimatedIconsTestApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    return MaterialApp(
+    return const MaterialApp(
       title: 'Animated Icons Test',
-      home: const Scaffold(
+      home: Scaffold(
         body: IconsList(),
       ),
     );