Part export improvements

- follow up fix for #22904 mostly cosmetic, but it seems better to show the user upfront what (s)he
will get when generating parts.
- fix #37696: sanitize filenames when exporting parts and while at it make the "Score_And_Parts" translatable.
    Also force the score's name as the first part of the name of the exported parts, regardless of which tab is the active one.