Open JDK Code convention coverage

This project aims to enhance Checkstyle by providing complete and up-to-date support for the OpenJDK Code Convention and the emerging OpenJDK Java Style Guidelines. The current implementation, based on the outdated sun_checks.xml configuration from 2004, lacks coverage for many modern rules and newly introduced Checkstyle modules. This project will systematically review both old and new guidelines, implement missing checks, refine existing configurations, and resolve known issues. The goal is to make OpenJDK coding conventions fully enforceable within Checkstyle, improving code quality and developer experience. Key deliverables include updating configurations, adding new modules where required, improving test coverage, and creating detailed documentation to clearly represent rule coverage and support levels.