Review the various tag listings

https://picard.musicbrainz.org/docs/tags/ and https://picard.musicbrainz.org/docs/mappings/ both list tags picard knows about and makes available, but neither list is complete. The first one is lacking at least originalyear and both are missing _albumartists (the tag mapping actually doesn't need to list _albumartists because it's not written to files, but I doubt that's clear to people not familiar with Picard) and the tag mapping is also missing artists.