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/card_swipe_test.dart

@@ -24,7 +24,10 @@ void main() {
       await tester.pumpAndSettle();
 
       // Check if removed properly.
-      expect(tester.widgetList(find.byType(Card)).length, lessThan(totalCards));
+      expect(
+        tester.widgetList(find.byType(Card)).length,
+        lessThan(totalCards),
+      );
     });
 
     testWidgets('All cards swiped out', (tester) async {
@@ -36,7 +39,10 @@ void main() {
       // Swipe out all cards.
       for (var i = 0; i < totalCards; i++) {
         // Swipe out one by one.
-        await tester.drag(find.byType(Card).last, const Offset(100.0, 0.0));
+        await tester.drag(
+          find.byType(Card).last,
+          const Offset(100.0, 0.0),
+        );
         await tester.pumpAndSettle();
       }