Deterministic DexCache in heap images.

Preload each slot in dex cache arrays with the candidate
entry with the lowest index.

Also fix a discrepancy where we used to keep an ArtField*
in the DexCache if we kept the declaring class rather than
based on the class referenced in the corresponding FieldId.
This can result in accessing a field through a FieldId with
an unresolved class as demonstrated by the regression test.

Test: 159-app-image-fields
Test: testrunner.py --host
Bug: 30627598
Change-Id: I34735047cb064ff462cd9859e86a61ddf8615ecd