Added the suppress error operator for @trigger_error()

[ezimuel]

This PR mitigate the usage of trigger_error() for E_USER_DEPRECATED using the @ suppress error operator.

The @ operator suppress the error message but it's still possible to catch it using a custom error handler, e.g. as follows:

set_error_handler(function ($errno, $errstr) {
    var_dump($errstr);
}, E_USER_DEPRECATED);

@trigger_error('Deprecation message here', E_USER_DEPRECATED);

Using this approach, we can give time to update the code related to the deprecation without breaking existing code (see https://github.com/babenkoivan/scout-elasticsearch-driver/issues/297 issue).

This is the same approach used by Symfony framework here.