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 `///`).

animations/test/basics/animated_builder_test.dart

@@ -16,7 +16,8 @@ void main() {
 
       // Get the initial color of the button.
       ElevatedButton button = tester.widget(find.byType(ElevatedButton));
-      WidgetStateProperty<Color?>? initialColor = button.style!.backgroundColor;
+      WidgetStateProperty<Color?>? initialColor =
+          button.style!.backgroundColor;
 
       // Tap the button.
       await tester.tap(find.byType(ElevatedButton));
@@ -24,7 +25,8 @@ void main() {
 
       // Get the updated color of the button.
       button = tester.widget(find.byType(ElevatedButton));
-      WidgetStateProperty<Color?>? updatedColor = button.style!.backgroundColor;
+      WidgetStateProperty<Color?>? updatedColor =
+          button.style!.backgroundColor;
 
       // Check if the color has changed.
       expect(initialColor, isNot(updatedColor));
@@ -35,7 +37,8 @@ void main() {
 
       // Get the initial color of the button.
       ElevatedButton button = tester.widget(find.byType(ElevatedButton));
-      WidgetStateProperty<Color?>? initialColor = button.style!.backgroundColor;
+      WidgetStateProperty<Color?>? initialColor =
+          button.style!.backgroundColor;
 
       // Tap the button to trigger the animation but don't wait for it to finish.
       await tester.tap(find.byType(ElevatedButton));
@@ -44,7 +47,8 @@ void main() {
 
       // Check that the color has changed but not to the final color.
       button = tester.widget(find.byType(ElevatedButton));
-      WidgetStateProperty<Color?>? changedColor = button.style!.backgroundColor;
+      WidgetStateProperty<Color?>? changedColor =
+          button.style!.backgroundColor;
       expect(initialColor, isNot(changedColor));
 
       // Wait for the animation to finish.