using GT utility classes for XML parsing/producing

[pmauduit]

See related PRs on GT/GS for the motivation:

• [GEOT-7898] Setup XMLUtils to assist in use of DefaultEntityResolver geotools/geotools#5639
• [GEOS-12110] Make use of XMLUtils for better integration with GeoTools Hints geoserver/geoserver#9502

Making use of GT utlity class to get XML-parsing related objects so that they are obtained from a centralized source.

[jodygarnett]

Hi @pmauduit I would like to merge to default-entity-resolver-check so that the upstream GeoTools integration tests can run.

With that in mind I will cherry pick your two commits over to that branch.

Q: Do you have access to geowebcache repo to work on public branch?

[pmauduit]

I'm missing 2 places in the code where I could not use GT's XMLUtils, I don't have access to GWC, so the current pr has been opened from my fork.

[jodygarnett]

This PR is supersseded by #1534 which makes use of public default-entity-resolver-check branch which is subject to integration tests.