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 `///`).

platform_design/lib/songs_tab.dart

@@ -55,10 +55,9 @@ class _SongsTabState extends State<SongsTab> {
 
     // Show a slightly different color palette. Show poppy-ier colors on iOS
     // due to lighter contrasting bars and tone it down on Android.
-    final color =
-        defaultTargetPlatform == TargetPlatform.iOS
-            ? colors[index]
-            : colors[index].shade400;
+    final color = defaultTargetPlatform == TargetPlatform.iOS
+        ? colors[index]
+        : colors[index].shade400;
 
     return SafeArea(
       top: false,
@@ -69,17 +68,15 @@ class _SongsTabState extends State<SongsTab> {
           song: songNames[index],
           color: color,
           heroAnimation: const AlwaysStoppedAnimation(0),
-          onPressed:
-              () => Navigator.of(context).push<void>(
-                MaterialPageRoute(
-                  builder:
-                      (context) => SongDetailTab(
-                        id: index,
-                        song: songNames[index],
-                        color: color,
-                      ),
-                ),
+          onPressed: () => Navigator.of(context).push<void>(
+            MaterialPageRoute(
+              builder: (context) => SongDetailTab(
+                id: index,
+                song: songNames[index],
+                color: color,
               ),
+            ),
+          ),
         ),
       ),
     );
@@ -117,8 +114,8 @@ class _SongsTabState extends State<SongsTab> {
         actions: [
           IconButton(
             icon: const Icon(Icons.refresh),
-            onPressed:
-                () async => await _androidRefreshKey.currentState!.show(),
+            onPressed: () async =>
+                await _androidRefreshKey.currentState!.show(),
           ),
           IconButton(
             icon: const Icon(Icons.shuffle),
@@ -168,6 +165,9 @@ class _SongsTabState extends State<SongsTab> {
 
   @override
   Widget build(context) {
-    return PlatformWidget(androidBuilder: _buildAndroid, iosBuilder: _buildIos);
+    return PlatformWidget(
+      androidBuilder: _buildAndroid,
+      iosBuilder: _buildIos,
+    );
   }
 }