Change Xcode project developmentRegion to 'en' and plist CFBundleDevelopmentRegion to DEVELOPMENT_LANGUAGE (#34293)

Eliminates 64-bit hardcoding for iOS test apps under dev/. This brings
them in line with the default iOS app templates.

Adds an initial integration test that:
1. captures laid-out widget size
2. focuses a text field to show the keyboard and resize the view
3. unfocuses the text field to dismiss the keyboard and resize the view
4. verify that the final widget size matches the initial size