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 `///`).

material_3_demo/lib/main.dart

@@ -75,20 +75,19 @@ class _AppState extends State<App> {
       theme: ThemeData(
         colorSchemeSeed:
             _colorSelectionMethod == ColorSelectionMethod.colorSeed
-                ? _colorSelected.color
-                : null,
-        colorScheme:
-            _colorSelectionMethod == ColorSelectionMethod.image
-                ? _imageColorScheme
-                : null,
+            ? _colorSelected.color
+            : null,
+        colorScheme: _colorSelectionMethod == ColorSelectionMethod.image
+            ? _imageColorScheme
+            : null,
         useMaterial3: _useMaterial3,
         brightness: Brightness.light,
       ),
       darkTheme: ThemeData(
         colorSchemeSeed:
             _colorSelectionMethod == ColorSelectionMethod.colorSeed
-                ? _colorSelected.color
-                : _imageColorScheme!.primary,
+            ? _colorSelected.color
+            : _imageColorScheme!.primary,
         useMaterial3: _useMaterial3,
         brightness: Brightness.dark,
       ),