backends/drm: make night light colorimetrically correct (only without ICC profiles)

Instead of just multiplying colors on the output, we also need to adapt them during
compositing, and tell clients using color management about it.
Without this, the primary colors would stay the same in absolute terms, just with
changed strength, but relative to the white point, aka how humans perceive it,
the color becomes more intense (even if darker) and changes.
With this, colors get moved around to be correct relative to the white point, which
makes night light change the image a lot less and makes the result easier on the eyes.

This is a bit like !6113, but it doesn't try to target any specific color temperature and thus is much smaller and doesn't need any UI changes.

without night light	master with night light at 2000K	this mr with night light at 2000K