Fretboard diagram feature requests

[avvvvve]

Split from #24912, where @scorster suggested these additional features for fretboard diagrams:

• Add an outline-only circle marker
• Option to control rotation of triangle when diagram is set to vertical/horizontal
• Move fingering entry directly beneath the diagram
• Allow optional alternate fingering on a separate field line
• Ability to specify the offset of fingerings and the fret number from the diagram
• Button to open the Style dialog from Properties
• The option to show the fret number at a specific fret in the diagram (not just the first fret)