Intent to Prototype: :has selector

[David Shin]

Summary: `:has()` selector lets authors select elements that anchor at least one element that matches its inner relative selector.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=418039

Standard Draft: https://drafts.csswg.org/selectors/#relational

Standard Positions: https://github.com/mozilla/standards-positions/issues/528

Platform Coverage: all

Preference: layout.css.has-selector.enabled

Other Browsers: Shipped - Chrome 105, Safari 15.4