Staff type editor: Fix disambiguation of parameters common to several groups.

- GenKeySig and ShowLedgerLines are shared by standard and percussion group
- SlashStyle is shared by all three groups

When saving the style, the current implementation overwrites the shared parameters with percussion params.
partial fix for #22996
Merge pull request #906 from mgavioli/Fix_stafftype_common_parameters

Staff type editor: Fix parameters common to several groups
fix #12079