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 `///`).

web_embedding/ng-flutter/flutter/lib/pages/counter.dart

@@ -24,11 +24,10 @@ class _CounterDemoState extends State<CounterDemo> {
             const Text('You have pushed the button this many times:'),
             ValueListenableBuilder(
               valueListenable: widget.counter,
-              builder:
-                  (context, value, child) => Text(
-                    '$value',
-                    style: Theme.of(context).textTheme.headlineMedium,
-                  ),
+              builder: (context, value, child) => Text(
+                '$value',
+                style: Theme.of(context).textTheme.headlineMedium,
+              ),
             ),
           ],
         ),