While the check for clutter_actor_has_mapped_clones clearly indicates
an intention to take clones into account, the following code
does not do so, likely because it predates the introduction of
clutter_actor_is_effectively_on_stage_view().
Switch to that newer API in order to take clones into account. This
avoids unnecessary wl_surface_send_enter() and wl_surface_send_leave()
events when entering the overview, reducing client work.
Note: wl_surface_send_leave() and wl_surface_send_enter() may trigger a buffer_scale or buffer_transform change. Depending on the client implementation this may result in a buffer resize, potentially a quite heavy operation.