src: add optional keep-alive object to SetImmediate

Adds the possibility to keep a strong persistent reference to
a JS object while a `SetImmediate()` call is in effect.

PR-URL: https://github.com/nodejs/node/pull/17183


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