Add methods for getting and setting individual color channels for all color spaces.

[LiamGallagher737]

Objective

Fixes #7746 except for making them const which is blocked on const float arithmetic.

Solution

Added a bunch more methods for getting and setting individual color channels for every color space.

Changelog

Added

• X_Y Get the Y value in linear X colorspace.
• set_X_Y Set the Y value in X colorspace.
• with_X_Y Returns this color with Y set to a new value in X colorspace.

For all the remaining channels and color spaces.

[coreh]

Looks mostly good! Left some very minor comments re: naming, method consolidation and behavior of setters, but after that, 👍 from me

[mockersf]

For the docs on all the set_ functions, it doesn't just return in the given kind, it also modified self.

I so much want to remove that file 🙁

[LiamGallagher737]

I so much want to remove that file 🙁

I personally think using a crate like palette is the way to go

[alice-i-cecile]

Fixed in #920. Choice was made fairly arbitrarily; feel free to submit follow-up PRs for nits.