Have image.FromUnparsedImage return a SourcedImage instead of types.Image
Have image.FromUnparsedImage return a SourcedImage instead of types.Image

This will allow us to add more methods to SourcedImage without breaking
external implementations of types.Image, if any.

Should not change behavior.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/image,containers/image