Update extern, built-ins, delegated, and __objref

`extern` works for objects, and functions and methods with or without
prototypes.

All the built-ins but `self` are `Name.Builtin` instead of
`Name.Builtin.Pseudo`, since the latter is only for implicit built-ins.

`delegated` is lexed as `Operator.Word`.

The parentheses after `__objref` and `defined` are lexed as `Operator`.