[css-color-adjust] color-invert CSS property

[chrishtr]

This would invert the existing colors on the property. e.g. white text becomes black, black background becomes white.

Motivation: helps site authors implement a dark theme incrementally.

More details here: https://github.com/minorninth/forced-dark-mode/blob/master/explainer.md#css-invert-property

@minorninth

[Malvoz]

To the CSSWG, I think #4623 and #2875 are ultimately discussing the same thing so perhaps want to merge into 1 issue.

[chrishtr]

I agree, they look like ultimately the same use case.

[fantasai]

Closing out in favor of #2875 which is a better proposal that can do the same thing, and more.