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 `///`).

.github/workflows/main.yml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        flutter_version: [stable, beta, master]
+        flutter_version: [stable, beta]
         os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
@@ -35,7 +35,7 @@ jobs:
       - uses: subosito/flutter-action@e938fdf56512cc96ef2f93601a5a40bde3801046
         with:
           channel: ${{ matrix.flutter_version }}
-      - run: ./tool/flutter_ci_script_${{ matrix.flutter_version }}.sh
+      - run: flutter pub get && dart tool/ci_script.dart
 
   # android-build:
   #   runs-on: ubuntu-latest
@@ -51,16 +51,16 @@ jobs:
   #         channel: stable
   #     - run: ./tool/android_ci_script.sh
 
-  ios-build:
-    runs-on: macos-latest
-    if: github.repository == 'flutter/samples'
-    steps:
-      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
-      - uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00
-        with:
-          distribution: 'zulu'
-          java-version: '17'
-      - uses: subosito/flutter-action@e938fdf56512cc96ef2f93601a5a40bde3801046
-        with:
-          channel: stable
-      - run: ./tool/ios_ci_script.sh
+  # ios-build:
+  #   runs-on: macos-latest
+  #   if: github.repository == 'flutter/samples'
+  #   steps:
+  #     - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+  #     - uses: actions/setup-java@c5195efecf7bdfc987ee8bae7a71cb8b11521c00
+  #       with:
+  #         distribution: 'zulu'
+  #         java-version: '17'
+  #     - uses: subosito/flutter-action@e938fdf56512cc96ef2f93601a5a40bde3801046
+  #       with:
+  #         channel: stable
+  #     - run: ./tool/ios_ci_script.sh