[X11] Handle reactivating an already focussed window

If we get a focus-in event on a window that kwin thinks should get focus, we mark it as active.

If we get a focus-in event on a window that kwin doesn't think should get focus it tries to activate a different window.

It can happen in the cause of trying to activate a different window that the list of pending windows and we try to focus that same window that initially had that focus-in event. In this case we want to activate it directly instead of calling focus and waiting for a reply.

Alternative fix to the reverted a0c4a8e7.

The existing unit test passes again