To make a frame clock tick as long as any of the associated surfaces
expect to receive ticks, make the surfaces inhibit freezing the clock,
instead of directly tell the frame clock to freeze itself.
This makes it so that as long as any surface using a certain frame clock
is not frozen (e.g. just received a frame event from the display
server), the frame clock will not be frozen.
With this, the frame clock is initiated as frozen, and won't be thawed
until any surface inhibits freeze. It will be frozen again, when every
surface has that previously inhibited freeze uninhibited freeze.
This api is meant to mimic xdg-popover.grab - we
show the surface, and dismiss it when we get events
on other surfaces. For foreign surfaces, the compositor
handles that for us; for our own, we check outselves
before delivering events to GTK.
Store popup parents separately from transient-for
parents, since these are separate concepts with
different behaviors. And we need the parent in
the frontend, so we can use it in the fallback
move-to-rect implementation.
We don't need the complicated wrapper system anymore,
since client-side windows are gone. This commit moves
all the vfuncs to GtkSurfaceClass, and changes the
backends to just derive their surface implementation
from GdkSurface.
