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/lib/src/misc/focus_image.dart

@@ -29,10 +29,12 @@ class Grid extends StatelessWidget {
         ),
         itemBuilder: (context, index) {
           return (index >= 20)
-              ? const SmallCard(imageAssetName: 'assets/eat_cape_town_sm.jpg')
+              ? const SmallCard(
+                  imageAssetName: 'assets/eat_cape_town_sm.jpg',
+                )
               : const SmallCard(
-                imageAssetName: 'assets/eat_new_orleans_sm.jpg',
-              );
+                  imageAssetName: 'assets/eat_new_orleans_sm.jpg',
+                );
         },
       ),
     );
@@ -50,7 +52,9 @@ Route _createRoute(BuildContext parentContext, String image) {
       ).chain(CurveTween(curve: Curves.ease)).animate(animation);
 
       return Stack(
-        children: [PositionedTransition(rect: rectAnimation, child: child)],
+        children: [
+          PositionedTransition(rect: rectAnimation, child: child),
+        ],
       );
     },
   );