Fixes issue of metadata/lyrics not updating when switching tracks

The issue is due to TrackMetadataModel::trackData not providing track data for tracks with Database ID of 0, which are tracks that are missing title metadata and are not added into elisaDatabase.db. In the fix, we remove the ID check. This introduces another issue, where in ContextView.qml onDatabaseIdChanged would not update the metadata/lyrics because the ID of tracks without metadata would be 0, and it wouldn't trigger the refresh of tracks changing. To alleviate this, we'll instead monitor the filename of the track playing, and when that changes, we update trackdata by the file URL.

On top of that, ContextView.qml now calls the proper function based on whether the track has a database id or not.

Concern: Does calling metaDataModel.initializeByUrl on onFileUrlChanged reduce performance compared to previous when it was called by IdAndUrl? A simple databaseId !== 0 check doesn't work here because the databaseId is updated later than the onFileUrlChanged is called, so you don't have the databaseId of the current track, rather the previous. Maybe there's a way to change the behaviour somewhere.

BUG: 436405