Fix 25423 - Issues with staff types in parts

Issues:
- Creating part(s) for a score adds a whole set of staff types for each created part
- Editing staff types gives unexpected results in part staves and may cause crash

Fixes:
- New staff types are created only for the root score, not for linked parts
- When staff types are edited, the updated staff types are set into the root score staves as well as in the staves linked to them.
Fix part tests: all reference scores contained the duplicated staff styles
Fixed GuitarPro tests.
Fix a regression for scores without parts (i.e. when root score staves are not linked to any other staff)
Merge pull request #843 from mgavioli/Fix_25423_Issues_with_staff_types_in_parts

Fix 25423 - Issues with staff types in parts