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/song_detail_tab.dart

@@ -42,38 +42,38 @@ class SongDetailTab extends StatelessWidget {
             // to build while the hero transition is mid-flight.
             //
             // It could either be specified here or in SongsTab.
-            flightShuttleBuilder: (
-              context,
-              animation,
-              flightDirection,
-              fromHeroContext,
-              toHeroContext,
-            ) {
-              return HeroAnimatingSongCard(
-                song: song,
-                color: color,
-                heroAnimation: animation,
-              );
-            },
+            flightShuttleBuilder:
+                (
+                  context,
+                  animation,
+                  flightDirection,
+                  fromHeroContext,
+                  toHeroContext,
+                ) {
+                  return HeroAnimatingSongCard(
+                    song: song,
+                    color: color,
+                    heroAnimation: animation,
+                  );
+                },
           ),
           const Divider(height: 0, color: Colors.grey),
           Expanded(
             child: ListView.builder(
               itemCount: 10,
-              itemBuilder:
-                  (context, index) => switch (index) {
-                    0 => const Padding(
-                      padding: EdgeInsets.only(left: 15, top: 16, bottom: 8),
-                      child: Text(
-                        'You might also like:',
-                        style: TextStyle(
-                          fontSize: 16,
-                          fontWeight: FontWeight.w500,
-                        ),
-                      ),
+              itemBuilder: (context, index) => switch (index) {
+                0 => const Padding(
+                  padding: EdgeInsets.only(left: 15, top: 16, bottom: 8),
+                  child: Text(
+                    'You might also like:',
+                    style: TextStyle(
+                      fontSize: 16,
+                      fontWeight: FontWeight.w500,
                     ),
-                    _ => const SongPlaceholderTile(),
-                  },
+                  ),
+                ),
+                _ => const SongPlaceholderTile(),
+              },
             ),
           ),
         ],
@@ -86,7 +86,10 @@ class SongDetailTab extends StatelessWidget {
   // ===========================================================================
 
   Widget _buildAndroid(BuildContext context) {
-    return Scaffold(appBar: AppBar(title: Text(song)), body: _buildBody());
+    return Scaffold(
+      appBar: AppBar(title: Text(song)),
+      body: _buildBody(),
+    );
   }
 
   Widget _buildIos(BuildContext context) {
@@ -101,6 +104,9 @@ class SongDetailTab extends StatelessWidget {
 
   @override
   Widget build(context) {
-    return PlatformWidget(androidBuilder: _buildAndroid, iosBuilder: _buildIos);
+    return PlatformWidget(
+      androidBuilder: _buildAndroid,
+      iosBuilder: _buildIos,
+    );
   }
 }