Dart 3.9 / Flutter 3.35 [first LLM release] (#2714)

I got carried away with Gemini and basically rewrote CI and the release
process for the new LLM reality. This work was largely completed by
Gemini.

- Bump all SDK versions to the current beta (3.9.0-0)
- Run `flutter channel beta`
- Wrote `ci_script.dart` to replace the bash scripts
- Converted repository to pub workspace #2499 
- Added llm.md and release.md
- Added redirect for deprecated Samples Index

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I have added sample code updates to the [changelog].
- [x] I updated/added relevant documentation (doc comments with `///`).

testing_app/test/favorites_test.dart

@@ -11,12 +11,12 @@ import 'package:testing_app/screens/favorites.dart';
 late Favorites favoritesList;
 
 Widget createFavoritesScreen() => ChangeNotifierProvider<Favorites>(
-      create: (context) {
-        favoritesList = Favorites();
-        return favoritesList;
-      },
-      child: const MaterialApp(home: FavoritesPage()),
-    );
+  create: (context) {
+    favoritesList = Favorites();
+    return favoritesList;
+  },
+  child: const MaterialApp(home: FavoritesPage()),
+);
 
 void addItems() {
   for (var i = 0; i < 5; i++) {
@@ -52,7 +52,9 @@ void main() {
       await tester.pumpAndSettle();
 
       // Get the total number of items available.
-      final totalItems = tester.widgetList(find.byIcon(Icons.close)).length;
+      final totalItems = tester
+          .widgetList(find.byIcon(Icons.close))
+          .length;
 
       // Remove one item.
       await tester.tap(find.byIcon(Icons.close).first);

testing_app/test/home_test.dart

@@ -9,9 +9,9 @@ import 'package:testing_app/main.dart';
 import 'package:testing_app/models/favorites.dart';
 
 Widget createHomeScreen() => ChangeNotifierProvider<Favorites>(
-      create: (context) => Favorites(),
-      child: MaterialApp.router(routerConfig: router()),
-    );
+  create: (context) => Favorites(),
+  child: MaterialApp.router(routerConfig: router()),
+);
 
 void main() {
   group('Home Page Widget Tests', () {
@@ -29,7 +29,11 @@ void main() {
       expect(find.text('Item 0'), findsOneWidget);
 
       // Fling i.e scroll down.
-      await tester.fling(find.byType(ListView), const Offset(0, -200), 3000);
+      await tester.fling(
+        find.byType(ListView),
+        const Offset(0, -200),
+        3000,
+      );
       await tester.pumpAndSettle();
 
       // Check if "Item 0" disappeared.