This will allow to copy the matrix as is and it is just cleaner to keep
the matrix in the same order specified by the mov standard (which is
also explicitly described in the documentation).
In order to preserve compatibility, flip the angle sign in the display API
av_display_rotation_set() and av_display_rotation_get(), and improve the
documentation mentioning the rotation direction.
Add AV_PKT_DATA_DISPLAYMATRIX and AV_FRAME_DATA_DISPLAYMATRIX as stream and
frame side data (respectively) to describe a display transformation matrix
for linear transformation operations on the decoded video.
Add functions to easily extract a rotation angle from a matrix and
conversely to setup a matrix for a given rotation angle.
Signed-off-by: Anton Khirnov <anton@khirnov.net>
