1. Make CupertinoSwitch use BoxShadow.toPaint() so that it respects
the `debugDisableShadows` flag.
2. Increase blue radius on debug banner
3. Only stroke "synthetic shadow" borders if elevation is positive.
In order to avoid checking binaries into flutter/flutter,
this comparator can be used to retrieve golden files from
a sibling flutter/goldens repository.
https://github.com/flutter/flutter/issues/16859
