Adds ai_recipe_generation sample (#2242)

Adding the demo app from my I/O talk. Because AI.

## 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 updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

---------

Co-authored-by: Brett Morgan <brett.morgan@gmail.com>

ai_recipe_generation/lib/widgets/star_rating.dart

@@ -0,0 +1,58 @@
+import 'package:flutter/material.dart';
+import 'package:material_symbols_icons/symbols.dart';
+
+typedef StarRatingCallback = void Function(int);
+
+class StartRating extends StatefulWidget {
+  const StartRating({
+    super.key,
+    required this.starColor,
+    required this.onTap,
+    this.initialRating = -1,
+  });
+
+  final Color starColor;
+  final int initialRating;
+
+  /// If [onTap] is not null, the stars are interactive
+  final StarRatingCallback? onTap;
+
+  @override
+  State<StartRating> createState() => _StartRatingState();
+}
+
+class _StartRatingState extends State<StartRating> {
+  late int selectedIdx;
+
+  @override
+  void initState() {
+    selectedIdx = widget.initialRating - 1;
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      children: [
+        ...List.generate(
+          5,
+          (index) => GestureDetector(
+            onTap: widget.onTap != null
+                ? () {
+                    setState(() {
+                      selectedIdx = index;
+                    });
+                    widget.onTap!(index);
+                  }
+                : null,
+            child: Icon(
+              Symbols.kid_star,
+              color: widget.starColor,
+              fill: selectedIdx >= index ? 1 : 0,
+            ),
+          ),
+        )
+      ],
+    );
+  }
+}