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 `///`).

ios_app_clip/lib/main.dart

@@ -37,7 +37,9 @@ class _DemoState extends State<Demo> {
   Widget build(BuildContext context) {
     return CupertinoApp(
       home: CupertinoPageScaffold(
-        navigationBar: const CupertinoNavigationBar(middle: Text('App Clip')),
+        navigationBar: const CupertinoNavigationBar(
+          middle: Text('App Clip'),
+        ),
         child: Center(
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,

ios_app_clip/pubspec.yaml

@@ -1,17 +1,15 @@
 name: ios_app_clip
 description: An example Flutter project that can build as an App Clip.
-
 publish_to: "none" # Remove this line if you wish to publish to pub.dev
-
 version: 1.0.0+1
+resolution: workspace
 
 environment:
-  sdk: ^3.7.0-0
+  sdk: ^3.9.0-0
 
 dependencies:
   flutter:
     sdk: flutter
-
   cupertino_icons: ^1.0.0
   device_info: ^2.0.3
 
@@ -20,5 +18,4 @@ dev_dependencies:
     path: ../analysis_defaults
   flutter_test:
     sdk: flutter
-
 flutter: