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 `///`).

desktop_photo_search/material/lib/src/unsplash/links.g.dart

@@ -31,7 +31,10 @@ class _$LinksSerializer implements StructuredSerializer<Links> {
       result
         ..add('self')
         ..add(
-          serializers.serialize(value, specifiedType: const FullType(String)),
+          serializers.serialize(
+            value,
+            specifiedType: const FullType(String),
+          ),
         );
     }
     value = object.html;
@@ -39,7 +42,10 @@ class _$LinksSerializer implements StructuredSerializer<Links> {
       result
         ..add('html')
         ..add(
-          serializers.serialize(value, specifiedType: const FullType(String)),
+          serializers.serialize(
+            value,
+            specifiedType: const FullType(String),
+          ),
         );
     }
     value = object.download;
@@ -47,7 +53,10 @@ class _$LinksSerializer implements StructuredSerializer<Links> {
       result
         ..add('download')
         ..add(
-          serializers.serialize(value, specifiedType: const FullType(String)),
+          serializers.serialize(
+            value,
+            specifiedType: const FullType(String),
+          ),
         );
     }
     value = object.downloadLocation;
@@ -55,7 +64,10 @@ class _$LinksSerializer implements StructuredSerializer<Links> {
       result
         ..add('download_location')
         ..add(
-          serializers.serialize(value, specifiedType: const FullType(String)),
+          serializers.serialize(
+            value,
+            specifiedType: const FullType(String),
+          ),
         );
     }
     return result;