WIP: Refactor of `Zend\Db\Exception` for 3.0.0

[ezimuel]

This is a task for refactoring Zend\Db\Exception using the type hints of PHP 7.2. You must work on the 3.0.0 branch.

If you change the API you should report it in the /3.0.0.md file.

Note: it's quite difficult to provide this code refactor without changing other classes. That means you should provide the refactoring without pass all the unit tests. In this phase is only important to have the unit tests running, so we you must focus only on fatal/parse errors.

[weierophinney]

This repository has been closed and moved to laminas/laminas-db; a new issue has been opened at laminas/laminas-db#15.