Segregated interfaces for Translator dependency of Validator component

This PR introduces segregated interfaces for the Translator dependency inside the Validator component.

This allows us to remove the hard dependency on the i18n component, and allows usage of the Validator with other translator systems via interface implementation.

A bridge is provided in the `Zend\Mvc\I18n` subcomponent; additionally, the MVC uses a translator factory that consumes that bridge to ensure the translator service works with all components.