Mark color-index at-media property as standard (#5408)
Mark color-index at-media property as standard (#5408)

https://drafts.csswg.org/mediaqueries-3/#color-index (Rec) and
https://drafts.csswg.org/mediaqueries-4/#color-index (CR) both define
the color-index at-media property as a standard feature.
mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data