This makes it possible to position client windows relative to their toplevel with the driver window rects only, without having to call into win32u to map window points. Updating the child window states whenever a window is moved will also let us to update the driver client-toplevel surface association in WindowPosChanged, for cases where the ancestor of a client surface is reparented.
-- v2: win32u: Pass all drivers window rects relative to the virtual screen. winex11: Handle ConfigureNotify for embedded window separately. win32u: Update children with a surface when the parent window moves. win32u: Lock the window when removing a vulkan surface from its list. win32u: Make sure vulkan windows have a pixel format selected. win32u: Pass window DPI rects in to MoveWindowBits. winemac: Remove MoveWindowBits driver entry.