fix pedal import/export for MusicXML

[rettinghaus]

This PR contains only the fixes to MusicXML import/export from #20219.

[Jojo-Schmitz]

Seems something is wrong with this PR (and its counterpart for master too):
Take the attached score,

export to MusicXML (attached too), import in Mu3 (the official way from Mu4 back to Mu3), gives:

Fatal error: line 108 column 73 Content of attribute type does not match its type definition: String content is not listed in the enumeration facet..

      <direction placement="below">
        <direction-type>
          <pedal type="resume" line="yes" sign="yes" default-y="-65.00"/>
          </direction-type>
        </direction>

It is the type="resume" it complains about
pedal.zip

Mu 4.1.1 doesn't complain, but screws up on import quite badly:

[Jojo-Schmitz]

Might not be related to this PR, as the issue exists with 4.2.0 Beta already, which IMHO is older than this PR's merge into the 4.2.0 branch?
Anyway, I've opened issue #20395 for this