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/animated_switcher.dart

@@ -48,8 +48,8 @@ class _AnimatedSwitcherDemoState extends State<AnimatedSwitcherDemo> {
         title: const Text('AnimatedSwitcher'),
         actions: [
           TextButton(
-            onPressed:
-                () => setState(() => container = generateContainer(++keyCount)),
+            onPressed: () =>
+                setState(() => container = generateContainer(++keyCount)),
             child: const Text('Change Widget'),
           ),
         ],
@@ -61,9 +61,8 @@ class _AnimatedSwitcherDemoState extends State<AnimatedSwitcherDemo> {
         child: AnimatedSwitcher(
           duration: const Duration(seconds: 1),
           child: container,
-          transitionBuilder:
-              (child, animation) =>
-                  ScaleTransition(scale: animation, child: child),
+          transitionBuilder: (child, animation) =>
+              ScaleTransition(scale: animation, child: child),
         ),
       ),
     );