Fix #321095: Support MusicXML 4.0 (export)

[lvinken]

Resolves:
https://musescore.org/en/node/328730
https://musescore.org/en/node/321095

Update the MusicXML version to 4.0 on export (second and final part of #321095). This prepares for future use of MusicXML 4.0 features.
Increase MusicXML MAX_NUMBER_LEVEL to 16 to match the 4.0 spec, which allows export of more overlapping hairpins etc.

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[Jojo-Schmitz]

First part (Import MusicXML 4.0, resp. update the validation schema files) was in #10060

[Jojo-Schmitz]

Any known (and good) reason why the vtests fail?`
I can't magine how that one-line change might have caused this.
Maybe a rebase solves this?

[Jojo-Schmitz]

This test is not yet used, or is it?

Adding void maxNumberLevel() { mxmlImportTestRef("testMaxNumberLevel"); } to https://github.com/musescore/MuseScore/blob/master/src/importexport/musicxml/tests/tst_mxml_io.cpp seems to work and pass

Edit 1: no, it doesn't...

Edit 2: it actually needs to be void maxNumberLevel() { mxmlMscxExportTestRef("testMaxNumberLevel"); }
(see below for some additional change that'd be needed to make it pass)

[Jojo-Schmitz]

Shouldn't this be 4.0?

Edit: That is what's keeping the unit test (if added, see above) from passing

[lvinken]

Fixed. Should have mentioned it yesterday: I wasn't done yet.

[Jojo-Schmitz]

Thanks.

[vpereverzev]

@lvinken looks like some of your recent changes has broken a couple of MXML unit tests.

see a876cef

Could you please take a look? For now, I had to temporarily disable them

[Jojo-Schmitz]

I've fixed the 3 failing tests as a 2nd commit to #10442

And it most likely isn't @lvinken's failt but mine, from #10586's 2nd commit, which adds/enables a bunch of those tests, which in turn were not prepared for MusicXML 4.0