Test against CGLIB memory leak for method injection

This commit introduces a test in XmlBeanFactoryTests that verifies that
CGLIB generated subclasses for method injected beans are reused across
bean factories for identical bean definitions. In other words, by
verifying that the same CGLIB generated class is reused for identical
bean definitions, we can be certain that Spring is no longer generating
identical, duplicate classes that consume memory in the VM.

Issue: SPR-10785, SPR-11420