Update user-defined error handler signature for PHP 8

Summary:
The errcontext parameter of the callback to handle errrors has been
deprecated in PHP 7.2 and removed in PHP 8.

Ref T2144

References:

• https://www.php.net/manual/en/function.set-error-handler.php

Maniphest Tasks: T2144

Differential Revision: https://devcentral.nasqueron.org/D3777