Add Color::lerp() convenience method for interpolating/mixing colors

[coreh]

🎃🦇🎃🦇🎃🦇🎃🦇🎃🦇🎃🦇

Objective

• I frequently find myself writing stuff like Color::AQUAMARINE * 0.6 + Color::DARK_GREEN * 0.4;
• It would be nice to have a convenience method for interpolating colors, just like we have in place for vectors;
• Actually, the expression above won't even produce the “correct” results, since it will take place in sRGB instead of linear RGB space, so it would be nice to have that taken care of for us;

Solution

• Add a Color::lerp() method.

---

Changelog

• Added a new Color::lerp() convenience method for interpolating colors. Colors are interpolated in linear RGB space for mathematically correct results.

[mockersf]

You often don't want a "mathematically correct" interpolation between colors, but a "perceptually correct" one: https://raphlinus.github.io/color/2021/01/18/oklab-critique.html

Marking as controversial, as lerping colors as been a hot topic for a while (#1402 #8189 or many discutions on discord)

[TimJentzsch]

A doc example/test could be nice here, otherwise LGTM :)

[rlidwka]

Perhaps, the function should take colorspace as 4th parameter?

That would decide how much user would care about performance (sRGB) vs perceptual correctness (Oklab).

[hymm]

#9698 also adds ability to lerp colors

[alice-i-cecile]

Can we add multiple doc aliases? If so, we should add "blend" as well.

[alice-i-cecile]

Suggested change

	/// **Note:** To ensure mathematically correct results, interpolation takes place in linear RGB
	/// Interpolation takes place in linear RGB

[alice-i-cecile]

This should be fixed now, with the addition of bevy_color.