Add AGENTS.md documentation for AI tools

This adds comprehensive documentation for AI agents and tools working with
the Eclipse SWT codebase. The new AGENTS.md file includes:

- Project overview and architecture details
- Complete build instructions (Maven/Tycho and native libraries)
- Repository structure and development workflows
- Essential development rules (OSGi, resource disposal, UI threading)
- Testing best practices and troubleshooting guidance
- AI agent-specific guidelines

CLAUDE.md is updated to reference AGENTS.md, following the pattern used
in eclipse.platform.ui repository.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: vogella