Flip/Update stereo surface buffers. Flips both the left and right
buffers simultaneously to ensure synchronization between the two.
Only applicable to window and layer surfaces with the DWCAPS_STEREO
or DLOP_STEREO option set; will fail with all other surfaces.
If no region is specified the whole surface is flipped,
otherwise blitting is used to update the region.
If surface capabilities don't include DSCAPS_FLIPPING,
this method has the effect to make visible changes
made to the surface contents.