Fix automatic unalignment of multiple voices in chords

Your idea

Keep centers of note heads vertically aligned, unless visible stems or close tones require displacement.

Problem to be solved

As described in the issue #20571, try to enter 3 notes as a chord in a violin score:

1. Voice 1, quarter C6
2. Voice 2, half C5
3. Voice 3, whole C4 (middle C)

It was expected to see all 3 notes aligned, but when C4 was entered, C5 note would be on the left from C4 and C6 .
In this case it was possible to get the desired alignmen by flipping stem direction of stemless whole note C6, but this is an additional manual action which should have been unnecessary.

Prior art

Tried the given example with two notation programs at hand, PriMus build 11978 and SIbelius 2023.5.1.
Both programs could align the same set of tones and voices automatically and correctly.

Reproduce the three-voice violin example described here and in issue #20571, using quarter C6, half C5, and whole C4. Compare the automatic note-head positions and verify the current workaround of flipping the stemless whole note. Done means the note heads remain vertically aligned without that manual action, while still displacing notes when stems or close tones require it.