wayland/actor-surface: Call ensure_size_valid() on shaped-texture

Use the new API to make sure the shaped texture has a valid size
during the next layout phase.

This is needed here because, quoting the previous commit:

When the texture size is invalidated using `invalidate_size()`, the new
size will only get calculated the next time `update_size()` is
called. This happens e.g. in `meta_shaped_texture_get_preferred_size()`
via `ensure_size_valid()`.

`update_size()` can chain up to `clutter_content_invalidate_size()`
as well as emitting a `size-changed` signal. If this happens during
layout, the result is a 'change the layout conditions during layout'
issue, causing heavy breakage in e.g. the Shell overview.

To fix this, expose `ensure_size_valid()` as API so callers can make
sure the texture has a valid size without creating redundant size
invalidations calls.

Note that if a buffer with a new size is attached we already trigger
`update_size()` explicitely, avoiding such situations.

Closes https://gitlab.gnome.org/GNOME/mutter/-/issues/1718

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1799>

src/wayland/meta-wayland-actor-surface.c

@@ -271,6 +271,8 @@ meta_wayland_actor_surface_real_sync_actor_state (MetaWaylandActorSurface *actor
       meta_surface_actor_reset_viewport_dst_size (surface_actor);
     }
 
+  meta_shaped_texture_ensure_size_valid (stex);
+
   META_WAYLAND_SURFACE_FOREACH_SUBSURFACE (surface, subsurface_surface)
     {
       MetaWaylandActorSurface *actor_surface;