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/features/prompt/prompt_model.dart

@@ -0,0 +1,66 @@
+import 'package:image_picker/image_picker.dart';
+
+import '../../util/filter_chip_enums.dart';
+
+class PromptData {
+  PromptData({
+    required this.images,
+    required this.textInput,
+    Set<BasicIngredientsFilter>? basicIngredients,
+    Set<CuisineFilter>? cuisines,
+    Set<DietaryRestrictionsFilter>? dietaryRestrictions,
+    List<String>? additionalTextInputs,
+  })  : additionalTextInputs = additionalTextInputs ?? [],
+        selectedBasicIngredients = basicIngredients ?? {},
+        selectedCuisines = cuisines ?? {},
+        selectedDietaryRestrictions = dietaryRestrictions ?? {};
+
+  PromptData.empty()
+      : images = [],
+        additionalTextInputs = [],
+        selectedBasicIngredients = {},
+        selectedCuisines = {},
+        selectedDietaryRestrictions = {},
+        textInput = '';
+
+  String get cuisines {
+    return selectedCuisines.map((catFilter) => catFilter.name).join(",");
+  }
+
+  String get ingredients {
+    return selectedBasicIngredients
+        .map((ingredient) => ingredient.name)
+        .join(", ");
+  }
+
+  String get dietaryRestrictions {
+    return selectedDietaryRestrictions
+        .map((restriction) => restriction.name)
+        .join(", ");
+  }
+
+  List<XFile> images;
+  String textInput;
+  List<String> additionalTextInputs;
+  Set<BasicIngredientsFilter> selectedBasicIngredients;
+  Set<CuisineFilter> selectedCuisines;
+  Set<DietaryRestrictionsFilter> selectedDietaryRestrictions;
+
+  PromptData copyWith({
+    List<XFile>? images,
+    String? textInput,
+    List<String>? additionalTextInputs,
+    Set<BasicIngredientsFilter>? basicIngredients,
+    Set<CuisineFilter>? cuisineSelections,
+    Set<DietaryRestrictionsFilter>? dietaryRestrictions,
+  }) {
+    return PromptData(
+      images: images ?? this.images,
+      textInput: textInput ?? this.textInput,
+      additionalTextInputs: additionalTextInputs ?? this.additionalTextInputs,
+      basicIngredients: basicIngredients ?? selectedBasicIngredients,
+      cuisines: cuisineSelections ?? selectedCuisines,
+      dietaryRestrictions: dietaryRestrictions ?? selectedDietaryRestrictions,
+    );
+  }
+}