Implement Reference.getReferent() intrinsic.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing --jit
Test: aosp_blueline-userdebug boots.
Test: run-gtests.sh
Test: testrunner.py --target --optimizing --jit
Bug: 170286013
Change-Id: I4762f7c1cf3d61de2215ec8f1d14be80289c2372
9 files changed