ServletContextInitializerBeans handles existing registration beans and
also creates initializers for existing Servlet, Filter, etc beans.
Debug logging has been added to this class to improve things in three
main areas:
- Distinguish between existing registration beans and those that are
created to wrap a Servlet or Filter bean
- Provide information about the resource (configuration class or XML)
that resulted in the creation of the bean
- Log information about EventListeners
Closes gh-2177
a1fbd1eeb5