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/integration_test/perf_test.dart

@@ -9,11 +9,13 @@ import 'package:testing_app/main.dart';
 
 void main() {
   group('Testing App Performance Tests', () {
-    final binding = IntegrationTestWidgetsFlutterBinding.ensureInitialized();
+    final binding =
+        IntegrationTestWidgetsFlutterBinding.ensureInitialized();
 
     // The fullyLive frame policy simulates
     // the way Flutter responds to animations.
-    binding.framePolicy = LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
+    binding.framePolicy =
+        LiveTestWidgetsFlutterBindingFramePolicy.fullyLive;
 
     testWidgets('Scrolling test', (tester) async {
       await tester.pumpWidget(const TestingApp());