during work on 6632124 (fix for 6429775 was incomplete) it become clear that we should reconsider the way
to handle _NET_FRAME_EXTENTS property. It looks like we should just listen changes of this property and update
insets according to these events, because, as 6632124 shown it is not safe to simply read this property at any
arbitrary time (because of possible thread races).

Another aspect we should reevaluate is whether we still need out "insets dancing" for modern WMs.