'Minimum distance' property for rests

[XiaoMigros]

This feature adds a purpose to the 'minimum distance' property for rests, controlling their vertical avoidance distance to chords or other rests. The distance is added onto the existing pre-calculated offset:

Here's an example with a large minimum distance of 2sp. The 'align with other rests' property has also offset the remaining rests in this example:

Crucially, this option allows for negative minimum distances, meaning it's possible to fix rests to a given line using a low minimum distance as well as the 'offset' property. This could improve MusicXML import as seen in #24971.

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[XiaoMigros]

or std::max(rest1->minDistance().val(), rest2->minDistance().val()) * lineDistance;

[mike-spa]

Minimum distance is one of the messiest things we have in our codebase. It's used in different ways, it means different things for different items, and for many of them means absolutely nothing and does nothing. It's one of those things that I'd like to nuke entirely and replace with something that makes more sense, at some point. So I'm a bit hesitant to introduce a new use for it.

Having said that, I actually do like this. It's certainly better than having it do nothing, and it is consistent with what it does for other items. So I'm inclined to approve this, if @its-not-nice approves the functionality.

[its-not-nice]

@XiaoMigros What real problem is this intended to solve?

[XiaoMigros]

The same problem that minimum distance solves e.g. for text elements: It adds the ability to configure vertical padding between elements, something I think should be available for multi-voice rests. I prefer working with minimum distance over offset as it scales better when further adjustments to the score are made. Introducing minimum distance for rests also has the added benefit of mitigating the above linked issue.