Refactor JAXB out

This repo currently uses com.fasterxml.jackson.module:jackson-module-jaxb-annotations, which is based on the pre-jakarta javax XML bind annotations. Pretty old.

Doing some searches, the blast radius is small:
https://github.com/search?q=repo%3Aopenrewrite%2Frewrite+jaxb&type=code
https://github.com/search?q=repo%3Aopenrewrite%2Frewrite+%22javax.xml.bind%22&type=code

Our MavenXmlMapper applies the JaxbAnnotationModule to its writeMapper, and not its readMapper, and the javax.xml.bind.annotation.XmlRootElement annotation is used in RawGradleModule and RawPom. Jackson has a native JacksonXmlRootElement replacement for that annotation, which should be an easy swap.

But even better, Claude and I suspect all this jaxb stuff is dead code anyway -- we only register the module on the write mapper, and those two classes are only deserialized, never serialized.

I think all this can be deleted?

Start by inspecting MavenXmlMapper and the JAXB annotations and usages in RawGradleModule and RawPom. Check whether the writeMapper registration and annotations are exercised, then run the existing test suite. Done means the obsolete JAXB dependency, module registration, and unused annotations are removed or replaced without breaking XML mapping.