This type unifies with any instance of classes that have a constructor which

* is public and
* unifies with the type used for type parameter `T`.

If a type parameter A is assigned to a type parameter B which is constrained to Constructible<T>, A must be explicitly constrained to Constructible<T> as well.

It is intended to be used as a type parameter constraint. If used as a real type, the underlying type will be Dynamic.