Infrastructure for obsolete methods

This adds some of the structures and functions needed to eventually
support obsolete methods. Specifically this adds the code to create
and iterate through the obsolete dex-cache maps of classes and
re-organizes the redefinition code to be more sensible and extensible.

Bug: 32369913
Test: ./test/run-test --host 902
Test: mma -j40 test-art-host

Change-Id: I93d60fa66e7512e8b059cdf42af8a56e93ef4bd7