This is a new try of mciqtz32's video window patch. Comparing to the previous !370, I added a lot of tests regarding the video window behavior. Some portion of the previous patch are dropped to avoid complexity, I'll add that part later.
-- v4: mciqtz32: Show the default video window when switching from another one. mciqtz32: Hide the default video window when switching to another one. mciqtz32: Reset the video size when changing video destination. mciqtz32: Fix MCI_DGV_WHERE_WINDOW behavior. mciqtz32: Correct video window behavior by creating default window. winmm/tests: Add tests for destination of video window. winmm/tests: Add tests for dimensions of video window. winmm/tests: Add tests for window style of video window. mciqtz32: Don't hide video window when stopping. winmm/tests: Add tests for visibility of video window.