Use real XML library for Effective POM

That is, build a DOM in memory and then serialize it. Use real DOM operations instead of brittle regex search and replace. Drop MavenXPP3Writer.

Maybe a general utility to convert a POM to a DOM/XOM/JDOM tree?

Worth exploring given how easy coding is getting with LLMs.

Start by locating the Effective POM generation and current MavenXPP3Writer usage. Review the available XML library options and existing project conventions; done should mean the POM is built and serialized through DOM operations without the brittle regex processing or MavenXPP3Writer.

Written by the indexing model from the issue text.