WIP: wayland: Properly handle async xdg-decoration updates

Currently, if a window switches between SSD and CSD, it is possible to encounter a "corrupted" state where the server-side decoration is wrapped around the window while it still has the client-side decoration.

The xdg-decoration protocol fixes this problem by saying that decoration updates are bound to xdg_surface configure events.

At the moment, kwin sort of applies decoration updates immediately. With this change, decoration updates will be done according to the spec.

If the compositor wants to remove the decoration, it sends a configure event to the client. After the configure event is acked and the surface is committed, the window decoration will be updated.

WIP because

• it breaks a lot of tests
• full screen mode is broken

Depends on kwayland-server!155 (merged)