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 `///`).

platform_design/lib/utils.dart

@@ -39,7 +39,8 @@ String generateRandomHeadline() {
     2 => '$artist releases ${capitalizePair(wordPairIterator.first)}',
     3 => '$artist talks about his ${nouns[_random.nextInt(nouns.length)]}',
     4 => '$artist talks about her ${nouns[_random.nextInt(nouns.length)]}',
-    5 => '$artist talks about their ${nouns[_random.nextInt(nouns.length)]}',
+    5 =>
+      '$artist talks about their ${nouns[_random.nextInt(nouns.length)]}',
     6 =>
       '$artist says their music is inspired by ${wordPairIterator.first.join(' ')}',
     7 =>
@@ -54,7 +55,9 @@ String generateRandomHeadline() {
 
 List<MaterialColor> getRandomColors(int amount) {
   return List<MaterialColor>.generate(amount, (index) {
-    return _myListOfRandomColors[_random.nextInt(_myListOfRandomColors.length)];
+    return _myListOfRandomColors[_random.nextInt(
+      _myListOfRandomColors.length,
+    )];
   });
 }