fix #282730: "Untitled"/"My First Score" does not respect locale page size

[Jojo-Schmitz]

No description provided.

[shoogle]

Couldn't this be MSCX? I don't think we show the thumbnail anywhere.

[Jojo-Schmitz]

Good idea, done.
Not sure though whether we'd need to convert preferences for older vesions to adjust to that change, nor how to do that.

[shoogle]

Ah, good point. That would involve finding the place where preferences are read during startup (I think in mscore/musescore.cpp), and then immediately afterwards saying:

if (preferences.startupFile == "My_First_Score.mscz")
      preferences.startupFile = "My_First_Score.mscx"

I believe that would be enough to ensure the new preference is written when MuseScore is closed too.

[Jojo-Schmitz]

I guess this should work

[IsaacWeiss]

While at it, any reason to keep the name "My_First_Score"? It's been a couple of years since that name was hidden in the UI: 3edf804

Also, I found where this issue was originally taken care of: acb0991

[Jojo-Schmitz]

Keeping the name doesn't harm though.
Those changes from acb0991, esp. the score->setPageFormat(*MScore::defaultStyle()->pageFormat()); are commented out with a TODO currently (and since 9a9dedf), so maybe just changing the template won't fix the issue at all?