src: turn JS stream into a full duplex

Remove unused methods for reading data from `JSStream` and add
those required for emitting data or an EOF event to the JS side,
in essentially the same way that `LibuvStreamWrap` does it.

PR-URL: https://github.com/nodejs/node/pull/16269


Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: James M Snell <jasnell@gmail.com>