Draft: opengl: make it possible to target an ICC profile with a color pipeline

This ensures that the optimizations we do for color pipelines are also applied to ICC profiles, and will allow us to apply the ICC profile in the item renderer in the future (which makes it possible to select an accuracy vs. performance tradeoff on a per window basis, and thus improve performance a lot for most use cases).

Because of those optimizations, this also improves accuracy of applying an ICC profile; in the autotest the maximum error went down from 5.83 to 4.12.