23799 annotations deleted when chordrests are

In 1.3, it was possible to attach chord symbols or other annotations to a note, then delete the note (either select & cut, or indirectly by extending length of previous note) and the annotation would remain.  Currently in 2.0, most annotations are deleted in this scenario (except annotations not associated with a chordrest, which is inconsistent).  This PR restores the 1.3 behavior: all annotations are preserved when chordrests are deleted.  It includes a new test.