MusicXML export: voltas only exported on first part and subtitle missing

[lgerenu]

Issue type

Import/export issue

Bug description

Exporting a multipart score with alternative volta repeats, the alternative markings are only placed in the first part. The measures are there but are not marked as alternatives.
Some meta information of the score is not placed in the MXL file (e.g. subtilte text).

Steps to reproduce

1. Create a new multipart score
2. Create some volta repeats
3. Export to MXL

Screenshots/Screen recordings

No response

MuseScore Version

4.2.1

Regression

I don't know

Operating system

Linux Mint 21.3 Virginia

Additional context

No response

[Jojo-Schmitz]

The missing voltas seem to be Mu3 regression, the missing subtitle is not, but that isn't related to parts, happens on the full score too, so would be a separate issue