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 `///`).

tool/flutter_ci_script_stable.sh

@@ -36,11 +36,10 @@ declare -ar PROJECT_NAMES=(
     "google_maps"
     "infinite_list"
     "ios_app_clip"
-    # TODO(ewindmill) For all the following 4 -- Uncomment when 3.34 goes stable. I updated too soon.
-    # "isolate_example"
-    # "material_3_demo"
-    # "platform_channels"
-    # "platform_design"
+    "isolate_example"
+    "material_3_demo"
+    "platform_channels"
+    "platform_design"
     "navigation_and_routing"
     "pedometer"
     "pedometer/example"
@@ -50,7 +49,7 @@ declare -ar PROJECT_NAMES=(
     "provider_shopper"
     "simple_shader"
     "simplistic_calculator"
-    # "simplistic_editor"
+    "simplistic_editor"
     "testing_app"
     "veggieseasons"
     "web_embedding/element_embedding_demo"