[Hellraiser28]

Follow-up to #42, reported by @nielsha in #42 (comment).

The bulk MusicBrainz lookup prefilled the search with the most common album artist, or the track artist when that was empty. On a compilation without an album artist tag every track artist appears once, so the first track's artist won and the release search found nothing.

Now the artist is chosen like this:

• If the files carry an album artist, that is used.
• Otherwise the track artists are compared by their main artist, ignoring guests after feat., ft., &, x, with, vs. or a comma. If no artist appears on more than half of the songs, the search starts with Various Artists, MusicBrainz' own name for compilations.
• A regular album with guest appearances keeps its artist, e.g. "Kendrick Lamar" for tracks credited "Kendrick Lamar feat. SZA".

Tested

• helpers.test.ts with 7 new tests. All MusicBrainz tests pass (38), ESLint, Prettier and tsc are clean.
• Against the MusicBrainz API with the query the modal builds: release:"Bravo Hits 1" AND artist:"Various Artists" finds 2 releases, with the first track's artist (Madonna) 0. Same for "Now That's What I Call Music! 50": 7 releases versus 0 with Robbie Williams.