Allow parentheses on subsets of notes in a chord

[miiizen]

Resolves: #18937

[bkunda]

Looking good @miiizen!

One important thing: we'll need to ensure that, no matter how the parentheses are displayed on a standard stave, the same display is also reflected in tab fret numbers on a linked tablature stave.

Screen.Recording.2026-01-05.at.11.09.41.am.mov

Let me know if this is something you'd prefer to do in a separate PR though (in order to unblock getting this first step merged).

Aside from this, we'll also need to refine the engraving styles a bit (collision avoidance, stroke thickness etc. – I know this is known, so I'm just spelling it out here so we don't forget about it).

[bkunda]

This is also worth noting: currently, adding parentheses to tablature fret numbers only adds them there (i.e. they don't get mirrored in the standard stave).

I think it might make sense to leave this behaviour as is, but ensure that the new rules for note grouping get applied to fret position numbers as well. Lmk if we need to chat about this further.

Screen.Recording.2026-01-05.at.11.13.23.am.mov

[miiizen]

@bkunda I'll have a look at these issues now and add the fixes to this PR.
Your second comment looks like a bug to me. Previously, user added parentheses were linked between TAB and standard staves. I think we should keep them linked!