FR: allow changing staff visibility mid-score

As discussed with Marc S. privately, there is currently no clean way to intersperse fragments of normal notation (including staff lines) and chord symbols (excluding staff lines, as covered in https://youtu.be/QiTpEwd-OuU) within the same system (line). This would be useful for partially arranged music which includes both exact notation and improvisation.

There is almost a way to have a staff switch between visible and invisible staff lines mid-score - the Staff Type Change ("S") element on the text palette. Add it to a measure, then click it and check the Inspector. There are a bunch of options for things you can change, but unfortunately, visibility of staff lines isn't one of them. So as suggested by Marc, I'm filing this issue to request adding that option.

For reference I'll also list below some workarounds Marc described, although they're not really relevant to this feature request:

1. Put an opaque white graphic over the measures you want invisible on the same system as the measures you want notated.
2. Do the notation part in a separate score and use the Image Capture tool (camera icon on toolbar) to capture the notation as an image, then paste that back onto the main score.
3. [Kind of crazy but actually works] Use two staves, one for notation, one for chords. But also use the "Cutaway" and "Hide when empty: Always" staff property for the notation staff. so the empty measures are automatcially made invisible, and the whole staff disappears when not needed. Now go to Format / Style, and on the Score tab, make Min. vertical distance -99 (which allows staves to overlap) and then on the Page tab, make Grand staff distance (or staff distance if the staves are in different instruments) -4 (which makes the staves overlap exactly).