* [RUNTIME] Introduce new object protocol.

This PR introduces a new object protocol to unify the node and object.
We also updated the existing runtime::vm code to make use of the new system.

Update to the node will be done in a follow up PR.

Other changes:

- Remove object related code in json serializer as that code logic was not complete
  and we have a separate serializer for VM, can revisit later.

* address review  comment

* Fix the child slot logic