For use in stubs.

see 9c7a3f8
see https://wiki.php.net/rfc/clone_with_v2
see php/php-src#18919

See php/php-src#18938

This method returns the named argument that matches the given `$name`,
or the positional (unnamed) argument that exists at the given `$position`,
otherwise, returns `null` for first-class callables or if no match is found.

We model this as an expression, just like all the other casts, even
though PHP treats (void) specially and makes it a statement. However,
it has a peculiar carve-out where (void) *is* allowed in for init
and loop expression lists (which only accept expressions, not
statements). As such, we need to model it as an expression.

This is deprecated in PHP 8.4.

clone($x, ) will parse as a function call, but be printed as
clone($x), which parses as a clone expression. The difference is
harmless.