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 `///`).

veggieseasons/lib/widgets/veggie_seasons_page.dart

@@ -19,7 +19,8 @@ class VeggieSeasonsPage<T> extends Page<T> {
 }
 
 class VeggieSeasonsPageRoute<T> extends PageRoute<T> {
-  VeggieSeasonsPageRoute(VeggieSeasonsPage<T> page) : super(settings: page);
+  VeggieSeasonsPageRoute(VeggieSeasonsPage<T> page)
+    : super(settings: page);
 
   VeggieSeasonsPage<T> get _page => settings as VeggieSeasonsPage<T>;