[php-src] PR #22971: Avoid truncation on null bytes in class and function names

Pull Request: https://github.com/php/php-src/pull/22971 Author: iliaal Follow-up to GH-22681. _class_string() and _function_string() still format the class name and the function name with %s, so Reflection*::__toString() cuts both at the first NUL byte. Anonymous class names embed one, directly and also inside the generated name of a closure declared in such a class. ```php $obj = new class { public function make(): Closure { return function () {}; } }; echo new ReflectionFunction($obj->make()); // Closure [ <user> public method {closure:class@anonymous ] { ``` master already appends the class name as a zend_string, so only the function name changes once this is merged up.