Fix arginfo for Reflection (Some parameters should be variadic)

[TysonAndre]

Fix arginfo for ReflectionClass::newInstance(), ReflectionFunction::invoke(), and ReflectionMethod::invoke()

E.g. var_export((new ReflectionMethod('ReflectionFunction', 'invoke'))->getParameters()[0]->isVariadic()); would previously output false. I expect it to output true

• See http://php.net/manual/en/reflectionfunction.invoke.php and http://php.net/manual/en/reflectionclass.newinstance.php

[carusogabriel]

@TysonAndre See #2492

[nikic]

We already made this change in the past and had to revert due to the BC break. This will have to wait until the next major version.