Exempt @font-face fonts from font limits; prefer them over local fonts

Our font limiting patch currently applies its limits to both local and remote fonts. Before #7937 (closed), this was fine, because we blocked remote fonts. However, now that we've decided to lift that block, we should exempt @font-face fonts from our limits, since they don't contribute to fingerprinting. Additionally, if they are present in a font rule that also contains local fonts, they should be used instead of local fonts.