Closing animation doesn't work for Firefox Wayland

Bugzilla issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1685928

Reproducible with weston-simple-egl with the following commit: https://gitlab.freedesktop.org/rmader/weston/-/commit/0ca6f0d8ed07a5643aa376cc114dae4644088d79 - note that the subsurface is destroyed after the xdg_toplevel.

Some investigation reveals:

• the subsurface MetaSurfaceActor is disposed too early
• meta_window_actor_wayland_rebuild_surface_tree() does not take freezing into account
• in wl_subsurface_destructor() unparents the subsurface MetaSurfaceActor from the MetaWindowActorWayland / parent in order to avoid destruction, also not taking freezing into account
• the main MetaSurfaceActor is owned by the corresponding MetaWindowActor

I think we'll need to rework (sub)surface actor ownership to solve this cleanly, as well as freezing MetaWindowActorWayland.