For asynchronous elements like a media source the paused state is rather
similar to the playing state. The most revelant difference is that
RequestSample commands are not immediately executed, but are scheduled
in an internal queue. As soon as playback is restarted, all pending
operations are submitted again (or they are discarded if playback is
stopped).

This patch implements such a queue, together with proper event emitting
when the media source is paused. Also, the characteristic
MFMEDIASOURCE_CAN_PAUSE is announced.

This patch is required for correct playback of some videos in Deep Rock
Galactic.
Signed-off-by: Giovanni Mascellani <gmascellani@codeweavers.com>
Signed-off-by: Huw Davies <huw@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>