ListenBrainzScrobbler: Report more info to ListenBrainz

Report music service, URL, and Spotify ID to ListenBrainz.
ListenBrainz accepts the music service in listen reports, in both a canonical domain format and a human-readable display name format. This commit makes Strawberry report both, for maximum flexibility. I've also set it up to report a shareable track URL for supported streaming services. I am already using this data in my homepage's "Now Playing" widget.

Fixes #1768

src/scrobbler/scrobblemetadata.h

@@ -45,6 +45,10 @@ class ScrobbleMetadata {
   QString musicbrainz_disc_id;
   QString musicbrainz_release_group_id;    // release_group_mbid
   QString musicbrainz_work_id;             // work_mbids
+  QString music_service;
+  QString music_service_name;
+  QString share_url;
+  QString spotify_id;
   qint64 length_nanosec;
 
   QString effective_albumartist() const { return albumartist.isEmpty() ? artist : albumartist; }