I was planning to have something like a JAXB/lib or lib/JDK9 within the zip distribution
having the needed files (4 jars) for JDK11 for the JAXB extension methods. I believe
we can change the startGroovy[.bat] scripts to set a system property, e.g. groovy.extras
or groovy.jaxb via JAVA_OPTS and add an extra entry something like below in
load !{groovy.home}/lib/${groovy.jaxb}/*.jar
The system property evaluates to empty if not found and the load
line is ignored if it doesn't point to an actual location. Then I think we can get rid
of the current "--add-modules" hack.

We might also need a groovy-jaxb-jdk9 or groovy-jaxb-deps maven
coordinate to also point to those jars to round out the simplification.


Cheers, Paul.