repairing XSD simple type definition defect

[wendellpiez]

In XSD generation, generated XSDs are defective when simple (atomic) types defined by OSCAL make references to other simple types -- the indirectly referenced OSCAL types (such as DateTimeWithTimeZone as a subtype of DateTime) are missing.

The XSD generation now revisits the list of types as many times as necessary to get the full list of all types referenced indirectly, from any given list (such as those referenced directly).

Committer Notes

XSD generation will be identical except when such dependent types are used.

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?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them? See Issue 223
• Have you written new tests for your core changes, as applicable? (Looked at unit testing, which looks fine.)
• Have you included examples of how to use your new feature(s)?
• Have you updated all website](https://pages.nist.gov/metaschema) and readme documentation affected by the changes you made? Changes to the website can be made in the website/content directory of your branch. n/a