Custom CSS Color 4 compliant css color parser

[kajkal]

Strict CSS color parser compliant with CSS Color 4 Specification.

maplibre-gl-js #2550

Main features:

• does not round numbers to integers from the range 0..255: rgb(50% 0% 0%) is equal to rgb(127.5 0 0) not rgb(127 0 0) or rgb(128 0 0)
• does not deviate from the syntax defined in the specification: rgb(50% 0 0) and rgb(50%,0% 0%) are treated as invalid

Differences with the specification:

• does not support grad, rad or turn angle units: hsl(.25turn 50% 50%) is not supported
• does not support none keyword: rgb(128 none none) is not supported
• does not support comments inside rgb/hsl functions: rgb(/* R */ 10%, /* G */ 20%, /* B */ 30%) is not supported

If anyone were to ask, I checked the regexes for catastrophic backtracking - they are safe.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[birkskyum]

@kajkal , thanks for this