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 `///`).

navigation_and_routing/lib/src/auth.dart

@@ -33,10 +33,9 @@ class BookstoreAuth extends ChangeNotifier {
   @override
   int get hashCode => _signedIn.hashCode;
 
-  static BookstoreAuth of(BuildContext context) =>
-      context
-          .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()!
-          .notifier!;
+  static BookstoreAuth of(BuildContext context) => context
+      .dependOnInheritedWidgetOfExactType<BookstoreAuthScope>()!
+      .notifier!;
 }
 
 class BookstoreAuthScope extends InheritedNotifier<BookstoreAuth> {