Issue468 metaschema enhancements

[wendellpiez]

Committer Notes

Implementing field/@in-xml on "markup-multiline" fields. The permitted values are with-wrapper (assumed by default) and unwrapped.

Changes:

• Metaschema XSD permits this attribute
• Metaschema Schematron validates its use (only on fields with as-type='markup-multiline
• Generated XSD now requires (or doesn't) the wrapper element
• Generated JSON Schema is unchanged
• Both conversion pathways support the feature

Still to do (at time of first draft PR):

• Documentation
• Stress testing including in combination with group-as features

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you squashed any non-relevant commits and commit messages? [instructions]
• Do all automated CI/CD checks pass?

[david-waltermire]

This has been integrated into PR #492.