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 `///`).

platform_channels/lib/src/method_channel_demo.dart

@@ -39,7 +39,9 @@ class _MethodChannelDemoState extends State<MethodChannelDemo> {
               FilledButton.icon(
                 onPressed: () async {
                   try {
-                    final value = await Counter.increment(counterValue: count);
+                    final value = await Counter.increment(
+                      counterValue: count,
+                    );
                     setState(() => count = value);
                   } catch (error) {
                     if (!context.mounted) return;
@@ -58,7 +60,9 @@ class _MethodChannelDemoState extends State<MethodChannelDemo> {
               FilledButton.icon(
                 onPressed: () async {
                   try {
-                    final value = await Counter.decrement(counterValue: count);
+                    final value = await Counter.decrement(
+                      counterValue: count,
+                    );
                     setState(() => count = value);
                   } catch (error) {
                     if (!context.mounted) return;