Add missing CSSFontFeatureValuesMap API feature (mdn#24166)

This PR adds the missing `CSSFontFeatureValuesMap` API. The data comes from the [mdn-bcd-collector](https://mdn-bcd-collector.gooborg.com) project (v10.12.2).

_Check out the [collector's guide on how to review this PR](https://github.com/openwebdocs/mdn-bcd-collector#reviewing-bcd-changes)._

Tests Used: https://mdn-bcd-collector.gooborg.com/tests/api/CSSFontFeatureValuesMap