[RFC] [Vote] Callable types (now: Callable prototypes)

Evening internals, With this message I'd like to go to vote with the Callable prototypes RFC targeted at 7.1: https://wiki.php.net/rfc/callable-types We've renamed it (previously was "Callable types") as RFC names often dictate how users will call the feature and I want it to be more accurate/descriptive. Also the reflection part was added although I'm short on time currently, so implementation for that will be ready later. (speaking of implementation, it also currently doesn't use cache_slots - also something I'll add when I have a little bit of time)