feat: support 4.0 in tests for XSLT and XQuery

[galtm]

This PR adds one compiler change and some simple tests for use of

• XSLT 4.0 in an XSLT SUT
• XQuery 4.0 in an XQuery SUT
• XPath 4.0 in a Schematron SUT or in an XSpec test for XSLT, XQuery, or Schematron

I ran the v4.0 tests interactively with Saxon-EE 12 from Oxygen, after modifying the "Run XSpec Test" transformation scenario to set saxon.custom.options to --allowSyntaxExtensions:on.

On the command line, I also ran a similar v4.0 XQuery test with BaseX 10.7, though I substituted the following for the last verification in the test. I'm having trouble finding an XPath 4.0 construct that is already implemented in both Saxon XQuery and BaseX.

<x:expect label="XPath 4.0 in the XSpec test also works"
	test="identity(4) eq 4"/>

After running external_xslt4.xspec from Oxygen, I checked that the compiled stylesheet specifies <xsl:map-entry key="'xslt-version'">4.0</xsl:map-entry> in the map of transform options.

Does #1729 require more than what's in this PR?

Puzzles (non-blocking)

1. Despite the Saxon documentation saying that transform() needs to specify the option xslt-version="4.0" to enable 4.0 support in the transformation being called, I was able to run external_xslt4.xspec in Oxygen even without the change in transform-options.xsl.
2. I am not sure if the Schematron usage is supposed to work (i.e., supported in Schematron itself), so consider that usage to be experimental. I logged this issue to inquire: Clarify support for XPath 4.0 or XSLT/XQuery 4.0 Schematron/schematron-enhancement-proposals#70

Presumed instructions for users

Tests for XSLT or Schematron

1. Set xslt-version="4.0" on<x:description>
2. Set the configuration property ALLOW_SYNTAX_EXTENSIONS (equivalently, use --allowSyntaxExtensions:on on the command line, or global/@allowSyntaxExtensions="true" in the configuration file). This step is copied from https://www.saxonica.com/documentation12/index.html#!v4extensions.

In Oxygen "Run XSpec Test" transformation scenario, you can accomplish step 2 by including --allowSyntaxExtensions:on in the saxon.custom.options parameter.

Tests for XQuery

Set xquery-version="4.0" on <x:description>