Add Spring XML Config Transpiler with comprehensive bean method generation

[groldan]

Implements a complete annotation processor that converts Spring XML bean definitions
to Java @configuration classes. The transpiler handles all major Spring XML patterns
found across GeoServer configurations including abstract bean inheritance, factory
methods, constructor injection, property wiring, and AOP proxy beans.

Key features include preservation of original XML structure in generated javadocs,
proper handling of bean aliases and circular references, support for component-scan
elements, and comprehensive test coverage with XMLUnit-based assertions that ignore
formatting differences and comments.

The implementation uses a visitor pattern for extensible code generation and
leverages Spring's own XML parsing infrastructure to ensure robust handling of
all namespace features while capturing the original DOM elements for documentation.