SPR-10630

    Allow BDRPostProcessors to register other BDRPPs
    
    Allow BeanDefinitionRegistryPostProcessor implementations to register
    beans that are themselves BeanDefinitionRegistryPostProcessors.
    
    Prior to this commit if a BeanDefinitionRegistryPostProcessor registered
    another BeanDefinitionRegistryPostProcessor its
    postProcessBeanDefinitionRegistry method would not be called.
    
    Issue: SPR-10630