xwayland: Send PresentCompleteModeSuboptimalCopy if dmabuf feedback was resent

If the dmabuf protocol's feedback object gave us a new list of
modifiers, send PresentCompleteModeSuboptimalCopy to the client
to inform them that they need to call GetSupportedModifiers.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
9 jobs for master in 2 minutes and 40 seconds (queued for 3 seconds)