Use modern markup for E_* constants (#4056)

- Indicate that E_STRICT is deprecated as of PHP 8.4.0
- explain the case where E_RECOVERABLE_ERROR can happen
- E_USER_ERROR should not be used any more.
- Rewording which removes personalization

Co-authored-by: Christoph M. Becker <cmbecker69@gmx.de>

Author: Girgias