Fix ReflectionType::__toString() BC break

Hello, our turn to be hit by this 7.1 BC break in Symfony: ReflectionType::__toString() now adds a ? in front of type hints where null is allowed by their default values. But since zend_bool is really an unsigned char, we have plenty of room to store and forward this semantic subtlety (nullable being set through ?Foo $arg vs Foo $arg = null) so that ReflectionType::__toString() can be accurate again, thus BC. See https://github.com/php/php-src/pull/2136 Thank for you consideration of this patch. Cheers, Nicolas