Detect single-voice chords and unis. regions on shared staves

Your idea

Currently, as soon as we have determined which instruments will fit on any given two-voice shared staff system, the voices remain fixed for the whole system.

We should automatically detect if there are regions where the instruments could be combined into a single voice (chords and/or unis.), despite the presence of two-voice regions on the system.

Problem to be solved

The same applies when more than two instruments share a single staff:

Prior art

No response

Additional context

We will want a Style > Shared staves option to set a threshold for when we consider combining notes into a single voice, to allow avoiding situations like this:

This and other options should be locally overridable via stave sharing changes.

Note that there will be cases where reducing the number of voices could allow more instruments to fit on the system than was first determined, by instruments moving in and out of shared voices. For now we can probably allow these more complex cases to be dealt with manually via Stave sharing changes.

An example that could fit on a single staff:

Checklist

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