Fix Shift+click selection between chord symbols and Roman numerals (Fixes #31410)

[pyonpyoco]

Resolves: #31410

This PR fixes the selection behavior where chord symbols and Roman numeral analysis were selected together when using click / Shift+click.

After this change, chord symbols, Roman numerals, and Nashville notation are treated as separate selectable elements for default click and Shift+click operations, while keeping the existing selection model otherwise unchanged.

Demo

2025-12-20.161633.mp4

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[XiaoMigros]

It seems easier to add a subtype property to harmony elements (equal to harmonytype). That reduces special logic and would allow for special selections in the select/more menu. See #20850 for an example of how to implement it (and what other methods are needed).

[pyonpyoco]

Thanks for the suggestion!
I added a subtype to the Harmony class and confirmed that this makes Shift+click and Select More behave consistently when selecting by subtype.
I didn’t add subtypeUserName() for now, since the UI already distinguishes the three harmony types correctly and I didn’t observe any issues. I kept the change minimal, but I’m happy to adjust this if needed.

2025-12-24.143938.mp4