Prior to this commit it was possible to configure the
DefaultListableBeanFactory used by the GenericWebApplicationContext
created by AbstractWebGenericContextLoader, but it was not possible to
completely replace the bean factory.
This commit introduces a new createContext() factory method in
AbstractWebGenericContextLoader which indirectly allows subclasses to
supply a custom DefaultListableBeanFactory implementation to the
GenericWebApplicationContext.
See gh-25600
Closes gh-28983
711820ec70