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_clean_packages.sh

@@ -0,0 +1,78 @@
+#!/bin/bash
+
+set -e
+
+flutter doctor -v
+
+declare -ar PROJECT_NAMES=(
+    "add_to_app/android_view/flutter_module_using_plugin"
+    "add_to_app/books/flutter_module_books"
+    "add_to_app/fullscreen/flutter_module"
+    "add_to_app/multiple_flutters/multiple_flutters_module"
+    "add_to_app/plugin/flutter_module_using_plugin"
+    "add_to_app/prebuilt_module/flutter_module"
+    "ai_recipe_generation"
+    "analysis_defaults"
+    "android_splash_screen"
+    "animations"
+    "asset_transformation"
+    "background_isolate_channels"
+    "code_sharing/client"
+    "code_sharing/server"
+    "code_sharing/shared"
+    "context_menus"
+    "deeplink_store_example"
+    "desktop_photo_search/fluent_ui"
+    "desktop_photo_search/material"
+    "dynamic_theme"
+    "experimental/federated_plugin/federated_plugin"
+    "experimental/federated_plugin/federated_plugin/example"
+    "experimental/federated_plugin/federated_plugin_macos"
+    "experimental/federated_plugin/federated_plugin_platform_interface"
+    "experimental/federated_plugin/federated_plugin_web"
+    "experimental/federated_plugin/federated_plugin_windows"
+    "experimental/pedometer"
+    "experimental/pedometer/example"
+    "experimental/varfont_shader_puzzle"
+    "experimental/web_dashboard"
+    "flutter_maps_firestore"
+    "form_app"
+    "game_template"
+    "gemini_tasks"
+    "google_maps"
+    "infinite_list"
+    "ios_app_clip"
+    "isolate_example"
+    "material_3_demo"
+    "navigation_and_routing"
+    "place_tracker"
+    "platform_channels"
+    "platform_design"
+    "platform_view_swift"
+    "provider_counter"
+    "provider_shopper"
+    "simple_shader"
+    "simplistic_calculator"
+    "simplistic_editor"
+    "testing_app"
+    "veggieseasons"
+    "web_embedding/element_embedding_demo"
+)
+
+echo "--- Running flutter clean and flutter pub get for each sample ---"
+
+for PROJECT_NAME in "${PROJECT_NAMES[@]}"
+    do
+      echo "== Cleaning '${PROJECT_NAME}' with Flutter clean =="
+      pushd "${PROJECT_NAME}"
+
+      # run `flutter clean` for project
+      flutter clean
+
+      # Grab packages.
+      flutter pub get
+
+      popd
+    done
+
+echo "--- Success ---"