surface-actor-x11: Only unredirect fullscreen windows for full damage

When deciding if a window should be unredirected because it was causing
fullscreen damage in the past, it was not considered whether the window
is still fullscreen. This could result in a floating window being
unredirected if it was chosen for unredirection because of
_NET_WM_BYPASS_COMPOSITOR = 1 and was previously fullscreened for >= 100
frames, long enough to change does_full_damage, before getting
unfullscreened.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2434
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2651>