Add static return type

RFC: https://wiki.php.net/rfc/static_return_type

The "static" type is represented as MAY_BE_STATIC, rather than
a class type like "self" and "parent", as

Add static return type

RFC: https://wiki.php.net/rfc/static_return_type

The "static" type is represented as MAY_BE_STATIC, rather than
a class type like "self" and "parent", as it has special
resolution semantics, and cannot be cached in the runtime cache.

Closes GH-5062.

show more ...