Switch to phpcs instead of php-cs-fixer.

Use CakePHP's ruleset.

I am hoping the team will be open to this change. While php-cs-fixer and phpcs achieve the same thing, cakephp's ruleset gives better defaults out of the box and avoids having to configure php-cs-fixer to achieve similar results. For e.g. ensuring declare(strict_types=1) are added at the top of all files.