gdk/wayland: Prefer wl_output_release() over wl_output_destroy()
By using wl_output_release(), GDK lets the compositor to clean up the output global more nicely.
For example, currently, most compositors remove the global and then destroy it later after N seconds expire. With this, the compositor could experiment with destroying the output global once all its resources are destroyed.
Includes parts of !5242 (merged)