[php-src] Issue #14860: Add support for serializing fake closures

Issue: https://github.com/php/php-src/issues/14860 Author: Girgias ### Description Fake closures are closures that reference an existing function and are most likely the result of using the First Class Callable syntax function_name(...). It not being serializable makes it harder to move from array/string callable to it. This limited support should be easier to implement than for arbitrary closures. Came up as a user-note: https://php.net/manual/en/functions.first_class_callable_syntax.php#129635