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 `///`).

simplistic_editor/test/main_screen_test.dart

@@ -71,7 +71,10 @@ void main() {
     );
 
     // About Dialog
-    expect(find.widgetWithIcon(IconButton, Icons.info_outline), findsOneWidget);
+    expect(
+      find.widgetWithIcon(IconButton, Icons.info_outline),
+      findsOneWidget,
+    );
     await tester.tap(find.widgetWithIcon(IconButton, Icons.info_outline));
     await tester.pumpAndSettle();
     expect(find.widgetWithText(Center, 'About'), findsOneWidget);