demux: mkv: handle rotation

If a display rotation is set to a MKV file, it must be taken into account.

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To reproduce the issue:

ffmpeg -display_rotation 90 -i big_buck_bunny.mp4 -c copy output.mp4
ffmpeg -display_rotation 90 -i big_buck_bunny.mp4 -c copy output.mkv

ffplay output.mp4    # ok
ffplay output.mkv    # ok

vlc output.mp4       # ok
vlc output.mkv       # ko (no rotation applied)

ffmpeg -i output.mkv -c copy remux.mp4
vlc remux.mp4        # ok