demux: mock: Add orientation option

Usage: ./vlc 'mock://<mock

 options>;video_orientation=<orientation>'

The video_orientation option is an integer representing the raw
values of video_orientation_t. Thus the range of possible values
is ORIENT_TOP_LEFT = 0 -> ORIENT_RIGHT_BOTTOM = 7.

Fix #25054

Signed-off-by: Alexandre Janniaux <ajanni@videolabs.io>