Add support for refreshing an ApplicationContext for AOT processing

[snicoll]

For us to be able to pre-process an ApplicationContext at build-time, we need a way to "refresh" it up to a point where it is ready to create bean instances, this includes:

• Prepare the BeanFactory
• Invoke BeanDefinitionRegistryPostProcessor implementations
• Invoke MergedBeanDefinitionPostProcessor implementations (note that these are special extensions of BeanPostProcessor that operates at the (merged) BeanDefinition level