This commit provides the necessary infrastructure to let components
contribute statements that are used to fully instantiate a bean
instance.
To ease code generation, a dedicated infrastructure to register bean
definition is provided in the o.s.beans.factory.generator package.
BeanDefinitionRegistrar offers a builder style API that provides a way
to hide how injected elements are resolved at runtime and let
contributors provide code that may throw a checked exception.
BeanInstanceContributor is the interface that components can implement
to contribute to a bean instance setup. DefaultBeanInstanceGenerator
generates, for a particular bean definition, the necessary statements
to instantiate a bean.
Closes gh-28047