Anchoring the ends of a line to two notes
It's quite common in piano music, that when the melody oscillates between the two staffs, the changes are marked with a line that follows it. (see below).
(however, most times the line is solid, not dotted)
I know that this is already possible in 1.2., but there, the line is a floating element. It's not anchored to the notes, so if there's some relayouting, page breaks... the thing will be messed up.
However, 1.2. already allows linking two notes with slurs across staves (crt+select the notes, then press 's'):
So I think it would the same, but with 'straight' slurs.
Possible idea: using all the same code used in the slurs but changing the order of the Bézier curves.
Related feature request: #17352: Glissando incorrectly positioned in cross staff notes
Note: the cross staff slur feature is currently not working well in the trunk.
See: #17350: Slur between notes to cross staff incorrectly positioned