Revert "Revert "Add hidden API to register/unregister QUIC conne..."

Revert submission 3561690-revert-3538339-SNUWWZJNJZ

Reason for revert: NewAPI error will be fixed by separate CL

Reverted changes: /q/submissionid:3561690-revert-3538339-SNUWWZJNJZ

Change-Id: Ia7367e9332f4d376bd0be4c03c095ee00de9177a
10 files changed