Proxy handler.has() does not have a receiver argument?

[#!/JoePea]

I really thing that because `has` is about detecting inherited
properties, the `receiver` parameter should be included. For things
like `ownKeys`, which are not about inheritance, then yeah, let's not
add receiver there.

I'm trying to implement my own multiple inheritance, but now I
stumbled on how to make it send back true for inherited keys when I
need to fork the lookup based on instances that are `WeakMap`ed to the
`receiver`.