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/icon_loading_indicator.dart

@@ -0,0 +1,98 @@
+import 'dart:async';
+import 'dart:math';
+
+import 'package:ai_recipe_generation/theme.dart';
+import 'package:flutter/material.dart';
+
+class IconLoadingAnimator extends StatefulWidget {
+  IconLoadingAnimator({
+    super.key,
+    required this.icons,
+    this.animationDuration,
+    this.millisecondsBetweenAnimations,
+  });
+
+  final List<IconData> icons;
+  final Duration? animationDuration;
+  final int? millisecondsBetweenAnimations;
+  final List<Color> colors = [
+    MarketplaceTheme.primary,
+    MarketplaceTheme.secondary,
+    MarketplaceTheme.tertiary,
+    MarketplaceTheme.scrim,
+    Colors.black87,
+  ];
+
+  @override
+  State<IconLoadingAnimator> createState() => _IconLoadingAnimatorState();
+}
+
+var rand = Random();
+
+class _IconLoadingAnimatorState extends State<IconLoadingAnimator> {
+  late List<IconData> notYetSeenIcons;
+  late IconData currentIcon;
+  late Color currentColor;
+  late Timer timer;
+
+  @override
+  void initState() {
+    super.initState();
+    notYetSeenIcons = widget.icons;
+
+    currentIcon =
+        notYetSeenIcons.removeAt(rand.nextInt(notYetSeenIcons.length));
+    currentColor = widget.colors[rand.nextInt(widget.colors.length)];
+
+    timer = Timer.periodic(
+      Duration(milliseconds: widget.millisecondsBetweenAnimations ?? 1000),
+      (timer) {
+        nextIcon();
+      },
+    );
+  }
+
+  void nextIcon() {
+    if (notYetSeenIcons.length == 1) notYetSeenIcons = widget.icons;
+    setState(() {
+      currentIcon =
+          notYetSeenIcons.removeAt(rand.nextInt(notYetSeenIcons.length));
+      currentColor = widget.colors[rand.nextInt(widget.colors.length)];
+    });
+  }
+
+  @override
+  void dispose() {
+    timer.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Container(
+      decoration: BoxDecoration(
+        shape: BoxShape.circle,
+        color: Colors.white,
+        border: Border.all(
+          color: MarketplaceTheme.focusedBorderColor,
+          width: 2,
+        ),
+      ),
+      child: AnimatedSwitcher(
+        duration: widget.animationDuration ?? const Duration(milliseconds: 200),
+        transitionBuilder: (child, animation) {
+          return ScaleTransition(
+            scale: animation,
+            child: child,
+          );
+        },
+        child: Icon(
+          size: 75,
+          color: currentColor,
+          key: Key(currentIcon.hashCode.toString()),
+          currentIcon,
+        ),
+      ),
+    );
+  }
+}