GitLab

* rgcn with new heterograph API

* apply_edge() forward for multi relation

* undoing changes from rgcn-hetero

* backward apply_edge(copy_u) added

* unittest for apply_edge(copy_e)

* Compatible with new PRs

* resolving conflict with master

* Bringing back change after resolving conflict

* minor

* minor
Co-authored-by: Israt Nisa <nisisrat@amazon.com>