Implement RetransformClasses

This CL implements basic support for the RetransformClasses function
and callbacks of the ClassFileLoadHook.

We do not yet support calling the ClassFileLoadHook events on first
load of class.

Bug: 32369913
Bug: 31684920

Test: mma -j40 test-art-host

Change-Id: I7959474f03f9903cc6f10ae3c06d9fd531ec7957