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 `///`).

animations/lib/src/misc/curved_animation.dart

@@ -91,13 +91,12 @@ class _CurvedAnimationDemoState extends State<CurvedAnimationDemo>
             style: Theme.of(context).textTheme.titleLarge,
           ),
           DropdownButton<CurveChoice>(
-            items:
-                curves.map((curve) {
-                  return DropdownMenuItem<CurveChoice>(
-                    value: curve,
-                    child: Text(curve.name),
-                  );
-                }).toList(),
+            items: curves.map((curve) {
+              return DropdownMenuItem<CurveChoice>(
+                value: curve,
+                child: Text(curve.name),
+              );
+            }).toList(),
             onChanged: (newCurve) {
               if (newCurve != null) {
                 setState(() {
@@ -114,13 +113,12 @@ class _CurvedAnimationDemoState extends State<CurvedAnimationDemo>
             style: Theme.of(context).textTheme.titleLarge,
           ),
           DropdownButton<CurveChoice>(
-            items:
-                curves.map((curve) {
-                  return DropdownMenuItem<CurveChoice>(
-                    value: curve,
-                    child: Text(curve.name),
-                  );
-                }).toList(),
+            items: curves.map((curve) {
+              return DropdownMenuItem<CurveChoice>(
+                value: curve,
+                child: Text(curve.name),
+              );
+            }).toList(),
             onChanged: (newCurve) {
               if (newCurve != null) {
                 setState(() {