Implement receiver side call handover api.

Bug: 65415068
Test: Manual

Design doc:
https://docs.google.com/document/d/1qY3oAzjff_4A1ttYb_CGrE_OwTRmXMG_KGsIuPT1ey8/edit#

Change-Id: I22cb1bc00c19ed1e4cf4b10baf5c0f661365785a
3 files changed