fix(utils): fix circular ref json.stringify

[GaetanCottrez]

Fix

Converting circular structure to JSON can occur during validation in the Validator class in the isObject method during this check: if (JSON.stringify(props) === JSON.stringify({})) return true;. The problem occurs when an Entity has props that contains another Entity or an array of Entities because the entities contain _domainEvents, which is a circular ref.

A new utils function named stringify allows handling circular ref similar to JSON.stringify.

#issue

4lessandrodev/type-ddd#414