Add a group QbzSelect to the Tracks toolbar. derive_tracks reorders the
visible rows by the group key (album+title, artist+album+title, or
title) so a group's tracks sit together. Visible group-header rows are
deferred until the list is virtualized (the list is a plain for today);
this is the group-ordering half, matching how Tauri's tracks tab uses
grouping as the ordering mechanism.
cc
vicrodh
2fce47bd06