RFC: color: expand the EDR concept to work for black levels as well

The current EDR system can not represent dynamic range extended in the blacks. If the black level is darker we have a higher dynamic range between black and SDR maximum white which is not the SDR range any more. Mapping to that range while assuming it's SDR results in wrong contrast. At the same time the extended dynamic range in the whites is relative to the range between the black level and the SDR maximum white so even the EDR is wrong if we have a different black level.

The proposed fix is to define both the SDR maximum white and minimum black levels relative to the dynamic range of the content for surfaces and the viewer for outputs.