Custom Decorator Support

Weld should support the addition of custom decorators.

The mechanics of adding them is:

• an Extension will register a Decorator implementation (say MyDecoratorBean) via AfterBeanDiscovery.addBean()
• MyDecoratorBean.getBeanClass() will indicate what is the decorator class (to enable/disable via beans.xml)
• getDecoratedTypes(), getDelegateType() and getDelegateQualifiers() will tell what beans can be decorated, as well as what delegate will be injected into the bean
• it is the responsibility of the custom decorator (via create()) to inject all references correctly, including the delegate. To that extent, the container must handle BeanManager.getInjectableReference() correctly

Note: at least for the initial implementation. we can make an assumption that create() for a Decorator bean is invoked only during the creation of a decorator chain.