RCSS: support hsl and hsla colors

[AmaiKinono]

To many web developers, HSL and HSLA colors are easier to work with. Here's a test in the sandbox:

[mikke89]

Great stuff, thanks a lot! Implementation looks good, and follows the style of the existing RGB-parsing, which is great.

I see that CSS allows some other variations of the spelling here, but it looks like this is the common spelling, so it makes sense to me to only allow this.

Only a couple minor things: It would be preferable to use use our built-in Array type instead of std::array, and format it with our clang-format config. Thanks!

I would also greatly appreciate if you could add documentation PR for this feature.

[AmaiKinono]

Only a couple minor things: It would be preferable to use use our built-in Array type instead of std::array, and format it with our clang-format config. Thanks!

Done. Other than this, I just read in https://www.w3.org/TR/css-color-3/#hsl-color that hue should be wrapped in [0, 360), so I've added that.

I would also greatly appreciate if you could add documentation PR for this feature.

Yes, this will come later ;)

[mikke89]

Perfect, thank you! A nice little quality-of-life improvement :)