gdk/wayland: freeze popups when hidden

gdk/wayland: freeze popups when hidden

Previously, there was an issue with glitching after showing/hiding a
popover that was not also destroyed. This was due to the popover having
an update_freeze_count of zero after hiding the surface.

That resulted in it's toplevel continuously dropping frames such as during
high-frame-rate scrolling in textviews. This problem is much more visible
on high-frame-rate displays such as 120hz/144hz.

With this commit, we freeze the frame clock of the popup until it is
mapped again.