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 `///`).

form_app/lib/main.dart

@@ -24,7 +24,8 @@ const double windowWidth = 480;
 const double windowHeight = 854;
 
 void setupWindow() {
-  if (!kIsWeb && (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
+  if (!kIsWeb &&
+      (Platform.isWindows || Platform.isLinux || Platform.isMacOS)) {
     WidgetsFlutterBinding.ensureInitialized();
     setWindowTitle('Form Samples');
     setWindowMinSize(const Size(windowWidth, windowHeight));
@@ -45,11 +46,10 @@ final demos = [
   Demo(
     name: 'Sign in with HTTP',
     route: 'signin_http',
-    builder:
-        (context) => SignInHttpDemo(
-          // This sample uses a mock HTTP client.
-          httpClient: mockClient,
-        ),
+    builder: (context) => SignInHttpDemo(
+      // This sample uses a mock HTTP client.
+      httpClient: mockClient,
+    ),
   ),
   Demo(
     name: 'Autofill',
@@ -130,5 +130,9 @@ class Demo {
   final String route;
   final WidgetBuilder builder;
 
-  const Demo({required this.name, required this.route, required this.builder});
+  const Demo({
+    required this.name,
+    required this.route,
+    required this.builder,
+  });
 }