ART: Correctly handle temporary classes in class-load events (4/3)

When a temporary class is given out in a ClassLoad event, all stored
references need to be fixed up before publishing a ClassPrepare event.

This CL handles objects stored in the heap as referents.

Bug: 31684920
Test: m test-art-host-run-test-912-classes
Change-Id: If140ecae675cd7bc648f622eaf200f8ad8b15438