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/lib/main.dart

@@ -64,36 +64,30 @@ class _MyAppState extends State<MyApp> {
       initialRoute: '/',
       routes: <String, Widget Function(BuildContext)>{
         '/': (context) => MyHomePage(onChangedPlatform: onChangedPlatform),
-        AnywherePage.route:
-            (context) => AnywherePage(onChangedPlatform: onChangedPlatform),
-        CustomButtonsPage.route:
-            (context) =>
-                CustomButtonsPage(onChangedPlatform: onChangedPlatform),
-        CustomMenuPage.route:
-            (context) => CustomMenuPage(onChangedPlatform: onChangedPlatform),
-        ReorderedButtonsPage.route:
-            (context) =>
-                ReorderedButtonsPage(onChangedPlatform: onChangedPlatform),
-        EmailButtonPage.route:
-            (context) => EmailButtonPage(onChangedPlatform: onChangedPlatform),
-        ImagePage.route:
-            (context) => ImagePage(onChangedPlatform: onChangedPlatform),
-        FieldTypesPage.route:
-            (context) => FieldTypesPage(onChangedPlatform: onChangedPlatform),
-        FullPage.route:
-            (context) => FullPage(onChangedPlatform: onChangedPlatform),
-        ModifiedActionPage.route:
-            (context) =>
-                ModifiedActionPage(onChangedPlatform: onChangedPlatform),
-        GlobalSelectionPage.route:
-            (context) =>
-                GlobalSelectionPage(onChangedPlatform: onChangedPlatform),
-        DefaultValuesPage.route:
-            (context) =>
-                DefaultValuesPage(onChangedPlatform: onChangedPlatform),
-        CascadingMenuPage.route:
-            (context) =>
-                CascadingMenuPage(onChangedPlatform: onChangedPlatform),
+        AnywherePage.route: (context) =>
+            AnywherePage(onChangedPlatform: onChangedPlatform),
+        CustomButtonsPage.route: (context) =>
+            CustomButtonsPage(onChangedPlatform: onChangedPlatform),
+        CustomMenuPage.route: (context) =>
+            CustomMenuPage(onChangedPlatform: onChangedPlatform),
+        ReorderedButtonsPage.route: (context) =>
+            ReorderedButtonsPage(onChangedPlatform: onChangedPlatform),
+        EmailButtonPage.route: (context) =>
+            EmailButtonPage(onChangedPlatform: onChangedPlatform),
+        ImagePage.route: (context) =>
+            ImagePage(onChangedPlatform: onChangedPlatform),
+        FieldTypesPage.route: (context) =>
+            FieldTypesPage(onChangedPlatform: onChangedPlatform),
+        FullPage.route: (context) =>
+            FullPage(onChangedPlatform: onChangedPlatform),
+        ModifiedActionPage.route: (context) =>
+            ModifiedActionPage(onChangedPlatform: onChangedPlatform),
+        GlobalSelectionPage.route: (context) =>
+            GlobalSelectionPage(onChangedPlatform: onChangedPlatform),
+        DefaultValuesPage.route: (context) =>
+            DefaultValuesPage(onChangedPlatform: onChangedPlatform),
+        CascadingMenuPage.route: (context) =>
+            CascadingMenuPage(onChangedPlatform: onChangedPlatform),
       },
     );
   }