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 `///`).

asset_transformation/grayscale_transformer/bin/grayscale_transformer.dart

@@ -11,10 +11,9 @@ int main(List<String> arguments) {
   // the `--input` option and one for the `--output` option.
   // `--input` is the original asset file that this program should transform.
   // `--output` is where flutter expects the transformation output to be written to.
-  final parser =
-      ArgParser()
-        ..addOption(inputOptionName, mandatory: true, abbr: 'i')
-        ..addOption(outputOptionName, mandatory: true, abbr: 'o');
+  final parser = ArgParser()
+    ..addOption(inputOptionName, mandatory: true, abbr: 'i')
+    ..addOption(outputOptionName, mandatory: true, abbr: 'o');
 
   ArgResults argResults = parser.parse(arguments);
   final String inputFilePath = argResults[inputOptionName];

asset_transformation/grayscale_transformer/pubspec.yaml

@@ -3,7 +3,7 @@ description: A sample command-line application.
 version: 1.0.0
 
 environment:
-  sdk: ^3.7.0-0
+  sdk: ^3.9.0-0
 
 dependencies:
   args: ^2.4.2