support JSR-303 bean validation in CDI beans

Consider a bean like

@SessionScoped
public class CurrentUser {
  @javax.validation.constraint.NotNull
  @javax.validation.constraint.Length(10)
  private String userId;

  ...
}

We could easily check this and invoke JSR-303 (if available) in the Producer<T>. Please note that for a custom Producer they have to care for it themselves.