This commit continues the work for fixing memory leaks resulting from
CGLIB subclass generation for beans relying on method injection.
- Set proxy callbacks on the CGLIB Factory (i.e., the instance) instead
of in the generated subclass (i.e., via the Enhancer).
- Convert private inner classes in CglibSubclassingInstantiationStrategy
to private static classes in order to avoid unnecessary coupling to
classes generated using CGLIB.
- Tidy up XmlBeanFactoryTests.
- Update logic in serializableMethodReplacerAndSuperclass() so that it
finally aligns with the decision made for SPR-356.
Issue: SPR-10785, SPR-356