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 `///`).

add_to_app/books/flutter_module_books/test/widget_test.dart

@@ -20,11 +20,15 @@ void main() {
     expect(mockHostApi.cancelCalls, 1);
   });
 
-  testWidgets('Pressing done calls the finish editing API', (tester) async {
+  testWidgets('Pressing done calls the finish editing API', (
+    tester,
+  ) async {
     MockHostBookApi mockHostApi = MockHostBookApi();
 
     await tester.pumpWidget(
-      MaterialApp(home: BookDetail(book: Book(), hostApi: mockHostApi)),
+      MaterialApp(
+        home: BookDetail(book: Book(), hostApi: mockHostApi),
+      ),
     );
 
     await tester.tap(find.byIcon(Icons.check));