partial fix for #25390: layout of 1.3 scores
fix #25648: manual positioning of note/chord should affect accidental
improve handling of rests
more tweaks; back out accidental change for now
update tests
improve handling of unisons and import of mirror property
fix notes_useroffset test; consider replacing it
fix merge conflicts
Merge pull request #889 from MarcSabatella/25390-layout-13

partial fix for #25390 - layout of "imported" 1.3 scores