Adds add2app Flutter module and an iOS project to run it. (#126)

experimental/add_to_app/example_module/pubspec.yaml

@@ -0,0 +1,30 @@
+name: example_module
+description: A simple module used to demo Flutter's Add2App features
+
+version: 1.0.0
+
+environment:
+  sdk: ">=2.4.0 <3.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  pedantic: ^1.8.0+1
+
+flutter:
+  uses-material-design: true
+
+  # This section identifies your Flutter project as a module meant for
+  # embedding in a native host app.  These identifiers should _not_ ordinarily
+  # be changed after generation - they are used to ensure that the tooling can
+  # maintain consistency when adding or modifying assets and plugins.
+  # They also do not have any bearing on your native host application's
+  # identifiers, which may be completely independent or the same as these.
+  module:
+    androidX: false
+    androidPackage: com.example.example_module
+    iosBundleIdentifier: com.example.exampleModule