Currently, there is a guarantee that a client, which is about to be removed,
is no longer in the stacking order(both in constrained and unconstrained)
when Workspace::removeClient is called. However, because the client gets
removed from m_allClients after clientRemoved is emitted, it can be
re-inserted back into the stacking order.
In general, the pattern is to do some work and then notify others about
what you've done by emitting a signal. In the case of Workspace::removeClient,
we emit clientRemoved way before the client actually gets removed.