fix #15373

[lvinken]

Force transposed pitch on MusicXML export by calling score()->cmdConcertPitchChanged() before and after export. Works OK as far as I can tell, please review. I am not completely sure there is no unforeseen interaction with the undo system, as I am not familiar with that.

[lasconic]

I would like the opinion of Werner about this change. I'm not a big fan because it links even more the import/export of MusicXML to mscore while it feels that it should be less linked to it and "closer" to libmscore. That could mean that the concert pitch state should be a Score property... Any opinion?

I believe undo should be ok. But any comment in this area is welcome too.

[lvinken]

I will have to investigate the alternatives. The current solution simply is the easiest one I could come up with. I do understand your concern.

Note that, IMHO, all importers / exporters should only depend on libmscore and not on mscore at all, as all they do is a data transformation between internal and external formats. The only possible exception being error reporting.

[Jojo-Schmitz]

I think that (meanwhile?) concert pitch is a score property. At least if I change the setting in the general style settings, the score gets marked dirty?

[lasconic]

Manually merged in 09d7822