window-actor: Add API to get a MetaWindowActor from a ClutterActor

Merged Robert Mader requested to merge rmader/mutter:subsurface-grabs into master

and make it so it returns the closest ancestry MetaWindowActor if it is a MetaSurfaceActor. Use it for events so Meta+Drag works on Wayland subsurfaces.

Fixes #487 (closed)

Edited by Robert Mader

Merge request reports