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/email_button_page.dart

@@ -22,9 +22,8 @@ class EmailButtonPage extends StatelessWidget {
   DialogRoute _showDialog(BuildContext context) {
     return DialogRoute<void>(
       context: context,
-      builder:
-          (context) =>
-              const AlertDialog(title: Text('You clicked send email!')),
+      builder: (context) =>
+          const AlertDialog(title: Text('You clicked send email!')),
     );
   }
 
@@ -64,7 +63,9 @@ class EmailButtonPage extends StatelessWidget {
                       editableTextState.textEditingValue;
                   final List<ContextMenuButtonItem> buttonItems =
                       editableTextState.contextMenuButtonItems;
-                  if (isValidEmail(value.selection.textInside(value.text))) {
+                  if (isValidEmail(
+                    value.selection.textInside(value.text),
+                  )) {
                     buttonItems.insert(
                       0,
                       ContextMenuButtonItem(