In preparation for per-monitor DPI awareness and display settings virtualization.
-- v2: win32u: Remove now unused NtUserIsWindowRectFullScreen call. winex11: Use the new fullscreen flag instead of NtUserIsWindowRectFullScreen. winewayland: Use the new fullscreen flag instead of NtUserIsWindowRectFullScreen. win32u: Pass whether a window is fullscreen to drivers WindowPosChanged. win32u: Use get_window_rect directly in clip_fullscreen_window. win32u: Use is_window_rect_fullscreen directly in clip_fullscreen_window. win32u: Use get_virtual_screen_rect directly within the module.