Making all the windows handled by the driver to be either GL/VK client surfaces, or top-level windows. This avoids leaking host windows into the Win32 space, and makes it possible to get rid of some remaining NtUserMapWindowPoints in `map_event_coords` for mouse input.
-- v7: winex11: Get rid of the now unnecessary foreign windows. winex11: Generate relative ConfigureNotify on parent ConfigureNotify events. winex11: Use the new host windows to register foreign window events. winex11: Keep track of the host windows children window rects. winex11: Keep track of the host windows relative rects. winex11: Keep track of the host window children of interest. winex11: Create host windows recursively up to root_window. winex11: Introduce a new struct host_window for host-only windows.