Add primaries, transfer, max_luma and video_colorspace arguments.
Allows tagging the colorspace of the overlay bitmap instead of assuming
sRGB. video_colorspace interprets the bitmap in the video's colorspace,
so it is tone mapped exactly like the video. max_luma overrides the
luminance peak of the bitmap. Currently only vo_gpu_next honors these
parameters. vo_gpu keeps its sRGB assumption regardless of the tag.
Fixes#10678
Kacper Michajłow
654e9382c0