[MU3 Backend] ENG-11: Articulations initially drawn incorrectly

[iveshenry18]

Resolves: ENG-11: Articulation marks initially drawn in wrong position

Specifically when dragging-and-dropping an XML file into MuseScore, the
articulations didn't layout correctly. This was due to a difference
between openScore (called when opening recent or from files) and
dropEvent (called when dropping).

This commit adds the style and layout-related lines to make sure score->layout is called after loading, which fixes the issue.

There appear to be further differences regarding migration, which may be worth further investigation.

This commit removes the partially-duplicated code in dropEvent and
rather calls openScore to handle loading, preventing discrepancies
between the two approaches.

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• I created the test (mtest, vtest, script test) to verify the changes I made

[cbjeukendrup]

Wouldn't it be better to just call openScore from dropEvent? That would avoid code duplication and discrepancies between the different ways to open a score.

[iveshenry18]

Wouldn't it be better to just call openScore from dropEvent?

I agree that this would be much cleaner (I winced as I copy-pasted code from one method to another). I was avoiding it because I'm not sure all the implications of the migration code, and I wasn't sure whether there was a great way to test for regressions, but I'll look into it!

[iveshenry18]

It didn't seem to introduce any regressions as far as I could tell, so I updated the commit to take that approach. Good call!