codec: videotoolbox: move functions to map color properties in vt_utils
requested to merge umxprime/vlc:umxprime/4.x/decoder/videotoolbox/move-functions-to-map-color-properties into master
Those functions can be useful in other places.
One useful case will be to attach color properties properly in the cvpx converter's output image buffers in a future fix without duplicating this mapping code.