specify Instance<T>#destroy()

In CDI-14, Pete mentioned that
> We would need to extend Instance<> with a void destroy(T instance); method.

Ouch, very true. This is desperately needed for destroying @Dependent and other not-normalscoped beans which got created via Instance<T>#get().

This currently creates memory leaks because we have no way to dispose the CreationalContext<T> used for creating this very bean. And since the CreationalContext<T> also holds references to all Interceptors, Decorators and subsequently injected beans, those won't be released neither.