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 `///`).

animations/test/misc/hero_animation_test.dart

@@ -58,7 +58,9 @@ void main() {
       // Final color should not be same as initial color.
       expect(
         (finalContainer.decoration as BoxDecoration).color,
-        isNot(equals((initialContainer.decoration as BoxDecoration).color)),
+        isNot(
+          equals((initialContainer.decoration as BoxDecoration).color),
+        ),
       );
     });
 
@@ -66,7 +68,9 @@ void main() {
       await tester.pumpWidget(createHeroAnimationDemoScreen());
 
       // Get the initial Screen.
-      final initialScreen = tester.firstWidget(find.byType(HeroAnimationDemo));
+      final initialScreen = tester.firstWidget(
+        find.byType(HeroAnimationDemo),
+      );
 
       // Tap on the GestureDetector.
       await tester.tap(find.byType(GestureDetector));