SharedReference serialization + deserialization (#180)

Add support for a `sharedId` property on serialized DOM nodes. This allows the node to be referenced across different globals e.g. from within a sandbox or from a script running in a different, same-origin, document.

Co-authored-by: Maksim Sadym <[email protected]>
Co-authored-by: James Graham <[email protected]>

Author: 3 people