Description:
------------
If you have a function with parameter with a default value preceding a required parameter (https://www.php.net/manual/en/migration80.deprecated.php), you get a deprecation warning (or notice?  not clear which it is).  However this warning doesn't get caught by set_error_handler() for some reason.

I first noticed this while using opcache (see https://bugs.php.net/bug.php?id=73665) but then noticed it repros even without opcache enabled.



Test script:
---------------
set_error_handler(function ($errno, $errstr, $errfile, $errline) {
    // This never hits
    die('caught in error handler');
});

function test($a = 1, $b ) {
  echo 'this executes';
}

// Displays "Deprecated: Required parameter $b follows optional parameter $a"
test(null, null);

Expected result:
----------------
I would expect the error handler to catch this warning.

Actual result:
--------------
Function executes and displays the warning.

If set_error_handler() is not supposed to catch this, is there another mechanism in PHP 8 to catch this warning at runtime?  It's often not practical to fix the references in 3rd party code that hasn't been updated for PHP 8 yet.