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 `///`).

background_isolate_channels/lib/main.dart

@@ -69,8 +69,8 @@ class _MyHomePageState extends State<MyHomePage> {
         .then(
           (sharedPreferences) => sharedPreferences.setBool('isDebug', true),
         );
-    final Future<Directory> tempDirFuture =
-        path_provider.getTemporaryDirectory();
+    final Future<Directory> tempDirFuture = path_provider
+        .getTemporaryDirectory();
 
     // Wait until the [SharedPreferences] value is set and the temporary
     // directory is received before opening the database. If
@@ -130,8 +130,9 @@ class _MyHomePageState extends State<MyHomePage> {
             padding: const EdgeInsets.symmetric(horizontal: 8.0),
             child: SearchBar(
               hintText: 'Search',
-              onChanged:
-                  _database == null ? null : (query) => _refresh(query: query),
+              onChanged: _database == null
+                  ? null
+                  : (query) => _refresh(query: query),
               trailing: const [Icon(Icons.search), SizedBox(width: 8)],
             ),
           ),

background_isolate_channels/lib/simple_database.dart

@@ -188,7 +188,9 @@ class _SimpleDatabaseServer {
         // [BinaryMessenger] that the Platform Channels will communicate with on
         // the background isolate.
         // ----------------------------------------------------------------------
-        BackgroundIsolateBinaryMessenger.ensureInitialized(rootIsolateToken);
+        BackgroundIsolateBinaryMessenger.ensureInitialized(
+          rootIsolateToken,
+        );
         _sendPort.send(const _Command(_Codes.ack, arg0: null));
       case _Codes.add:
         _doAddEntry(command.arg0 as String);

background_isolate_channels/pubspec.yaml

@@ -1,12 +1,13 @@
 name: background_isolate_channels
 description: A new Flutter project.
+resolution: workspace
 
 publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 
 version: 1.0.0+1
 
 environment:
-  sdk: ^3.7.0-0
+  sdk: ^3.9.0-0
 
 dependencies:
   cupertino_icons: ^1.0.2
@@ -23,6 +24,5 @@ dev_dependencies:
     path: ../analysis_defaults
   flutter_test:
     sdk: flutter
-
 flutter:
   uses-material-design: true