fix #23799: annotations deleted with chordrests

Segment annotations are currently deleted if the last chordrest in that
segment is deleted - either because you selected a region containing
this chordrest and hit Cut/Delete or because you lengthened a previous
chordrest to subsume this one.  But the 1.3, and expected, behavior is
that annotations remain even when chordrests are deleted.
add tests

test new behavior - lengthening note and clearing selection preserve
chord symbols
Merge pull request #589 from MarcSabatella/23799-lengthen-deletes-text

23799 annotations deleted when chordrests are