This PR contributes to https://github.com/flutter/flutter/issues/130459
### Description
- Updates `examples/api/lib/widgets/animated_size/animated_size.0.dart` API example by using `SizedBox` to size the surrounding of the `FlutterLogo` while setting the constant `FlutterLogo` size. This was done because `FlutterLogo` already has size animation under the hood, and the main goal of this example is to show `AnimatedSize` usage
- Adds test for `examples/api/lib/widgets/animated_size/animated_size.0.dart`
