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 `///`).

game_template/lib/src/ads/ads_controller.dart

@@ -36,11 +36,10 @@ class AdsController {
   void preloadAd() {
     // TODO: When ready, change this to the Ad Unit IDs provided by AdMob.
     //       The current values are AdMob's sample IDs.
-    final adUnitId =
-        defaultTargetPlatform == TargetPlatform.android
-            ? 'ca-app-pub-3940256099942544/6300978111'
-            // iOS
-            : 'ca-app-pub-3940256099942544/2934735716';
+    final adUnitId = defaultTargetPlatform == TargetPlatform.android
+        ? 'ca-app-pub-3940256099942544/6300978111'
+        // iOS
+        : 'ca-app-pub-3940256099942544/2934735716';
     _preloadedAd = PreloadedBannerAd(
       size: AdSize.mediumRectangle,
       adUnitId: adUnitId,

game_template/lib/src/ads/banner_ad_widget.dart

@@ -150,10 +150,9 @@ class _BannerAdWidgetState extends State<BannerAdWidget> {
       // https://developers.google.com/admob/android/test-ads. When ready,
       // you replace this with your own, production ad unit ID,
       // created in https://apps.admob.com/.
-      adUnitId:
-          Theme.of(context).platform == TargetPlatform.android
-              ? 'ca-app-pub-3940256099942544/6300978111'
-              : 'ca-app-pub-3940256099942544/2934735716',
+      adUnitId: Theme.of(context).platform == TargetPlatform.android
+          ? 'ca-app-pub-3940256099942544/6300978111'
+          : 'ca-app-pub-3940256099942544/2934735716',
       size: size,
       request: const AdRequest(),
       listener: BannerAdListener(