Use non-constant luminance coefficients so newer ffmpeg will render hdr animations.

Also fix the order of the mastering display info. This can be backported.

BUG:520669 has a testing file to try out.

@dkazakov , I made an MR of this because I didn't want to cause a surprise that the matrix coefficients had changed. They're now non-constant luminance, because ffmpeg doesn't support constant luminance anymore, but the whys and hows I do not understand.