Request: Parse ALBUMARTIST separately to ARTIST for Vorbis tags

[SigmoidDev]

It would be very handy if there were separate fields for artist and albumArtist as currently they are both parsed into the same field (at least for Vorbis tags). Looking at vorbis_comment.dart, parseVorbisComment contains the following, which could easily be split into two cases:

case 'ARTIST' || "ALBUMARTIST": metadata.artist.add(value); break;