Input by duration: disallow adding duplicate notes to chords

[avvvvve]

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

Case 1 - FIXED in #26468

1. Add some notes to your score, then click away to exit note input mode
2. Select one of the notes
3. Press M to enter input by duration mode. The pitch stays set to the selected note's pitch (expected)
4. Press a duration key matching the selected note
5. Another of the same note is added, as if it were a chord (unexpected)

If you exit input by duration mode and then repeat steps 2-5, you can keep adding more of the same note to the "chord" (shown in the video below at 0:07 onward).

Case 2 (using MIDI keyboard) - FIXED in #26794

1. Press M
2. On MIDI keyboard, press C
3. Input quarter note
4. On MIDI keyboard, release C
5. Go back to initial position with Left
6. On MIDI keyboard, press C
7. Input quarter note

Expected behavior: If the pitch, duration, and voice you're entering match the note already selected, don't add another note.

Supporting files, videos and screenshots

Screen.Recording.2025-02-11.at.7.48.00.PM.mov

What is the latest version of MuseScore Studio where this issue is present?

This PR: #26367

Regression

No.

Operating system

macOS 15

Additional context

No response

Checklist

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• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible