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/main.dart

@@ -0,0 +1,122 @@
+import 'package:ai_recipe_generation/util/device_info.dart';
+import 'package:ai_recipe_generation/util/tap_recorder.dart';
+import 'package:camera/camera.dart';
+import 'package:device_info_plus/device_info_plus.dart';
+import 'package:firebase_core/firebase_core.dart';
+import 'package:flutter/gestures.dart';
+import 'package:flutter/material.dart';
+import 'package:google_generative_ai/google_generative_ai.dart';
+import 'package:provider/provider.dart';
+
+import 'features/prompt/prompt_view_model.dart';
+import 'features/recipes/recipes_view_model.dart';
+import 'firebase_options.dart';
+import 'router.dart';
+import 'theme.dart';
+
+late CameraDescription camera;
+late BaseDeviceInfo deviceInfo;
+
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Firebase.initializeApp(
+    options: DefaultFirebaseOptions.currentPlatform,
+  );
+  deviceInfo = await DeviceInfo.initialize(DeviceInfoPlugin());
+  if (DeviceInfo.isPhysicalDeviceWithCamera(deviceInfo)) {
+    final cameras = await availableCameras();
+    camera = cameras.first;
+  }
+
+  runApp(const MainApp());
+}
+
+class MainApp extends StatefulWidget {
+  const MainApp({super.key});
+
+  @override
+  State<MainApp> createState() => _MainAppState();
+}
+
+class _MainAppState extends State<MainApp> {
+  late GenerativeModel geminiVisionProModel;
+  late GenerativeModel geminiProModel;
+  @override
+  void initState() {
+    const apiKey =
+        String.fromEnvironment('API_KEY', defaultValue: 'key not found');
+    if (apiKey == 'key not found') {
+      throw InvalidApiKey(
+        'Key not found in environment. Please add an API key.',
+      );
+    }
+
+    geminiVisionProModel = GenerativeModel(
+      model: 'gemini-pro-vision',
+      apiKey: apiKey,
+      generationConfig: GenerationConfig(
+        temperature: 0.4,
+        topK: 32,
+        topP: 1,
+        maxOutputTokens: 4096,
+      ),
+      safetySettings: [
+        SafetySetting(HarmCategory.harassment, HarmBlockThreshold.high),
+        SafetySetting(HarmCategory.hateSpeech, HarmBlockThreshold.high),
+      ],
+    );
+
+    geminiProModel = GenerativeModel(
+      model: 'gemini-pro',
+      apiKey: const String.fromEnvironment('API_KEY'),
+      generationConfig: GenerationConfig(
+        temperature: 0.4,
+        topK: 32,
+        topP: 1,
+        maxOutputTokens: 4096,
+      ),
+      safetySettings: [
+        SafetySetting(HarmCategory.harassment, HarmBlockThreshold.high),
+        SafetySetting(HarmCategory.hateSpeech, HarmBlockThreshold.high),
+      ],
+    );
+
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final recipesViewModel = SavedRecipesViewModel();
+
+    return TapRecorder(
+      child: MultiProvider(
+        providers: [
+          ChangeNotifierProvider(
+            create: (_) => PromptViewModel(
+              multiModalModel: geminiVisionProModel,
+              textModel: geminiProModel,
+            ),
+          ),
+          ChangeNotifierProvider(
+            create: (_) => recipesViewModel,
+          ),
+        ],
+        child: SafeArea(
+          child: MaterialApp(
+            debugShowCheckedModeBanner: false,
+            theme: MarketplaceTheme.theme,
+            scrollBehavior: const ScrollBehavior().copyWith(
+              dragDevices: {
+                PointerDeviceKind.mouse,
+                PointerDeviceKind.touch,
+                PointerDeviceKind.stylus,
+                PointerDeviceKind.unknown,
+              },
+            ),
+            home: const AdaptiveRouter(),
+          ),
+        ),
+      ),
+    );
+  }
+}