wayland: Fix the popover race workaround

wayland: Fix the popover race workaround

The Wayland backend has a hack to work around
a race with popover mapping: If the surface size
changes before the initial configure, we hide and
show the surface. Unfortunately, the code was doing
this in a way that is externally observable (by
listening for surface state changes), and popovers
were observing it and hiding themselves in response.

Avoid this by not going through the GDK frontend
code for this.