wayland: switch to xdg interface

The xdg_shell interface replaces the old wl_shell interface. It provides more
features and is simpler to use.

The protocol file is distributed by mpv and the header and binding code is
generated from the protocol file. This is for some reason recommended.

If no xdg_shell is avaible the window won't show up.
wayland_common: rework state handling & fullscreen

Remove vo_wayland_{fullscreen,ontop,border} functions.

Fullscreen handling is done in window_set_fullscreen and the other 2 are not
implemented and used.