This is the sequel of request #15020: while it is now possible to use representations marked as immutable it is not made mandatory/enforced. This is the goal of this request.

A nice side-effect of enforcing it, is that it will naturally force the structures holding data used to be build the representations to be immutable/mutation free. This is a good thing because it makes those structures easier to reason about and makes it harder to introduce some bad architecture patterns.