[VOTE] Add array_is_list(array $array): bool

Hi internals,

Voting on https://wiki.php.net/rfc/is_list has started. The vote closes on 2020-01-20.

After discussion, the function name and signature was changed to array_is_list(array $array): bool
to avoid confusion with the possibility of earlier name choices conflicting with hypothetical future list-like types,
and to make it obvious that using it on an ArrayObject/SplDoublyLinkedList is probably a mistake
(throw an ordinary parameter TypeError for non-arrays).

• See https://externals.io/message/112560#112757

Thanks,
-Tyson