Fixes#6347
- Fixed MusicBrainz Lucene query formatting in
`MusicBrainzAPI.format_search_term()` (lowercase + trim + escape Lucene
special chars).
- Fixed `plugins.musicbrainz:extra_tags` support by mapping `alias` and
`tracks` into MusicBrainz search fields.
- Adjusted logging to make MusicBrainz API logs visible under the shared
`beets` logger (and removed an unused per-module logger in
`beetsplug.bpd`).
