Schematron support upgrade with refurb (Recreated with rewritten history)

[nikitawootten-nist]

WIP towards updating Schematron support for Metaschema

• Updated metaschema-composition-check.sch Schematron now works with schxslt XSLT transpiler not only the old 'Skeleton' transpiler
• XProcs for applying this Schematron to metaschema are provided - one for each transpiler under XML Calabash
• A copy of schxslt is provided (but not as a submodule - revisit this?) for a complete runtime

In this PR I edited the history to remove the schxslt zip file and vendored content.

Committer Notes

With this commit we have several more options for providing Schematron support.

More work may need to be done to optimize Schematron outputs (using the new svrl-reduce.xsl filter), then integrating.

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• 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?
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Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you included examples of how to use your new feature(s)?
• Have you updated all website and readme documentation affected by the changes you made? Changes to the website can be made in the website/content directory of your branch.

[nikitawootten-nist]

Merging with verbal approval of the team 🎉