Pass xsl:include in Schematron through to the compiled stylesheet

[vincentml]

This change allows using xsl:include in a Schematron to include an XSLT file. This currently works in oXygen 19.1 but does not work in the Schematron Skeleton XSLTs. A use case for this is to import an XSLT that contains a library of custom functions. It is currently possible to include xsl:function definitions in a Schematron though only in the main Schematron file, so this change allows for better organization and reusability.

<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
    <sch:ns uri="function-library" prefix="lib"/>
    <xsl:include href="function-library.xsl"/>
    <sch:pattern>
        <sch:rule context="example">
            <sch:assert test="lib:check(.)">custom function check</sch:assert>
        </sch:rule>
    </sch:pattern>
</sch:schema>

[vincentml]

The new sch:extends[@href] element might accomplish the same goal. I will have to try this possibly better alternative.