user32/win32k: Implement "ghost window"

We should implement "ghost window".

https://msdn.microsoft.com/en-us/library/windows/desktop/ms644927.aspx

If a top-level window stops responding to messages for more than several seconds, the system considers the window to be not responding. In this case, the system hides the window and replaces it with a ghost window that has the same Z order, location, size, and visual attributes. This allows the user to move it, resize it, or even close the application. However, these are the only actions available because the application is actually not responding. When in the debugger mode, the system does not generate a ghost window.