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 `///`).

desktop_photo_search/fluent_ui/lib/src/unsplash/position.g.dart

@@ -87,8 +87,16 @@ class _$Position extends Position {
       (new PositionBuilder()..update(updates))._build();
 
   _$Position._({required this.latitude, required this.longitude}) : super._() {
-    BuiltValueNullFieldError.checkNotNull(latitude, r'Position', 'latitude');
-    BuiltValueNullFieldError.checkNotNull(longitude, r'Position', 'longitude');
+    BuiltValueNullFieldError.checkNotNull(
+      latitude,
+      r'Position',
+      'latitude',
+    );
+    BuiltValueNullFieldError.checkNotNull(
+      longitude,
+      r'Position',
+      'longitude',
+    );
   }
 
   @override