Color maths 4

[lynn-lumen]

Objective

• Fixes Add color animation support #12202

Solution

• This PR implements componentwise (including alpha) addition, subtraction and scalar multiplication/division for some color types.
• The mentioned color types are Laba, Oklaba, LinearRgba and Xyza as all of them are either physically or perceptually linear as mentioned by @alice-i-cecile in the issue.

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Changelog

• Scalar mul/div for LinearRgba may modify alpha now.

Migration Guide

• Users of scalar mul/div for LinearRgba need to be aware of the change and maybe use the .clamp() methods or manually set the alpha channel.

[NthTensor]

Looking great!

I'll just repeat what I said on discord here as well: Eventually I want to have better support for non-linear alpha blending modes (perhaps with some sort of Blend<LinearRgba, BlendMode> or perhaps not). I also want to make converting vectors into colors a bit easier. Ditto with math on cylindrical color spaces. None of that needs to block this PR.

Mostly what I see remaining is bike-shedding about the specific implementation of the color algebra. The operations don't need to be perfect but they do need to be well defined.

[NthTensor]

Rereading #12163 (comment) it looks like we might want to exclude alpha from scalar multiplication/division.

[IQuick143]

Rereading #12163 (comment) it looks like we might want to exclude alpha from scalar multiplication/division.

That would break splines, as it breaks distributivity over addition.

[NthTensor]

After looking at some other color crates, I am less concerned about the alpha component. We've got enough approvals for merge, and this isn't marked controversial so I am adding the tag.