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 `///`).

context_menus/test/global_selection_page_test.dart

@@ -5,43 +5,49 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  testWidgets('Gives correct behavior for all values of contextMenuBuilder', (
-    tester,
-  ) async {
-    await tester.pumpWidget(const MyApp());
+  testWidgets(
+    'Gives correct behavior for all values of contextMenuBuilder',
+    (
+      tester,
+    ) async {
+      await tester.pumpWidget(const MyApp());
 
-    // Navigate to the GlobalSelectionPage example.
-    await tester.dragUntilVisible(
-      find.text(GlobalSelectionPage.title),
-      find.byType(ListView),
-      const Offset(0.0, -100.0),
-    );
-    await tester.pumpAndSettle();
-    await tester.tap(find.text(GlobalSelectionPage.title));
-    await tester.pumpAndSettle();
-    expect(
-      find.descendant(
-        of: find.byType(AppBar),
-        matching: find.text(GlobalSelectionPage.title),
-      ),
-      findsOneWidget,
-    );
+      // Navigate to the GlobalSelectionPage example.
+      await tester.dragUntilVisible(
+        find.text(GlobalSelectionPage.title),
+        find.byType(ListView),
+        const Offset(0.0, -100.0),
+      );
+      await tester.pumpAndSettle();
+      await tester.tap(find.text(GlobalSelectionPage.title));
+      await tester.pumpAndSettle();
+      expect(
+        find.descendant(
+          of: find.byType(AppBar),
+          matching: find.text(GlobalSelectionPage.title),
+        ),
+        findsOneWidget,
+      );
 
-    // Right click on the plain Text widget.
-    TestGesture gesture = await tester.startGesture(
-      tester.getCenter(
-        find.descendant(of: find.byType(ListView), matching: find.byType(Text)),
-      ),
-      kind: PointerDeviceKind.mouse,
-      buttons: kSecondaryMouseButton,
-    );
-    await tester.pump();
-    await gesture.up();
-    await gesture.removePointer();
-    await tester.pumpAndSettle();
+      // Right click on the plain Text widget.
+      TestGesture gesture = await tester.startGesture(
+        tester.getCenter(
+          find.descendant(
+            of: find.byType(ListView),
+            matching: find.byType(Text),
+          ),
+        ),
+        kind: PointerDeviceKind.mouse,
+        buttons: kSecondaryMouseButton,
+      );
+      await tester.pump();
+      await gesture.up();
+      await gesture.removePointer();
+      await tester.pumpAndSettle();
 
-    // The default context menu is shown with a custom button.
-    expect(find.byType(AdaptiveTextSelectionToolbar), findsOneWidget);
-    expect(find.text('Back'), findsOneWidget);
-  });
+      // The default context menu is shown with a custom button.
+      expect(find.byType(AdaptiveTextSelectionToolbar), findsOneWidget);
+      expect(find.text('Back'), findsOneWidget);
+    },
+  );
 }