ART: Correctly handle temporary classes in class-load events (1/3)

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 as global references.

Bug: 31684920
Test: m test-art-host-run-test-912-classes
Change-Id: I2f79c7943e13c0db9ad7cb9cd60450ff6373be4f