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 `///`).

add_to_app/fullscreen/flutter_module_fullscreen/pubspec.yaml

@@ -0,0 +1,35 @@
+name: flutter_module_fullscreen
+description: An example Flutter module.
+version: 1.0.0+1
+resolution: workspace
+
+environment:
+  sdk: ^3.9.0-0
+
+dependencies:
+  flutter:
+    sdk: flutter
+  provider: ^6.0.2
+
+dev_dependencies:
+  analysis_defaults:
+    path: ../../../analysis_defaults
+  flutter_test:
+    sdk: flutter
+  flutter_driver:
+    sdk: flutter
+  espresso: ">=0.2.0 <0.5.0"
+
+flutter:
+  uses-material-design: true
+
+  # This section identifies your Flutter project as a module meant for
+  # embedding in a native host app.  These identifiers should _not_ ordinarily
+  # be changed after generation - they are used to ensure that the tooling can
+  # maintain consistency when adding or modifying assets and plugins.
+  # They also do not have any bearing on your native host application's
+  # identifiers, which may be completely independent or the same as these.
+  module:
+    androidX: true
+    androidPackage: dev.flutter.example.flutter_module
+    iosBundleIdentifier: dev.flutter.example.flutterModule