[MU4] Fix #329470: Wrong/missing transpositioning on MusicXML import

[Jojo-Schmitz]

If the optional element "diatonic" is missing, calculate it from "chromatic".

Resolves: https://musescore.org/en/node/329470
Same issue in 3.x.

Also adds/enables all (most?) available MusicXML unit tests (commenting out those that fail, working on those is out of score of this PR).

[Jojo-Schmitz]

@lvinken: please review

[lvinken]

As indeed diatonic is optional but chromatic is required, the code change is correct. I apparently overlooked the possibility of missing diatonic, which led to an invalid interval in my implementation. Thanks for fixing this.

Note that a missing chromatic would be caught by the schema validation.

A testfile would be a nice addition, to prevent this requirement from being missed in future.

[Jojo-Schmitz]

OK, I'll drop the check for the mandatory "chromatic", as it is caught elsewhere already.

[Jojo-Schmitz]

I see a testChangeTranspose.xml, which we might use for this, by making a copy (e.g. testChangeTranspose-no-diatonic.xml) and removing the optional diatonic, but I don't see where that test is actually run, so don't know where and how to add it (or them both)
That test is used in 3.x (as void changeTranspose() { mxmlIoTest("testChangeTranspose"); } in tst_mxml_io.cpp), but apparently not in master? Added it back and it does pass the test too.
Can't get the new test void changeTranspose() { mxmlIoTestRef("testChangeTranspose-no-diatonic"); } to work though.

[Jojo-Schmitz]

As far as I'm concerned this PR is ready for getting merged ;-)

[lvinken]

Looks good to me, thanks.