Auto merge of #550 - yvt:feat-lazyproto, r=jdm
Add a "lazy prototype" parameter to `NewProxyObject`
This PR introduces a new parameter `aLazyProto` to the `NewProxyObject`, where its value is passed to `js::ProxyOptions::setLazyProto`.
Setting the lazy proto property allows proxy handlers to provide dynamic prototype objects. This is necessary for maybe-cross-origin objects, whose [`[[GetPrototypeOf]]`][1] internal methods have a dynamic behavior.
[1]: https://html.spec.whatwg.org/multipage/history.html#location-getprototypeof
