Improve reachabilityFence

This avoids retaining the argument Object unnecessarily, at the cost
of making it even more ridiculously expensive. That's OK, since the
accompanying art CL ensures that it will not be called in a normal
production setting.

This unbreaks 036-finalizer with the added reachabilityFence.

Bug: 72698200

Test: art/test/run-test --host --prebuild --interpreter --verify-soft-fail --64 --build-with-javac-dx  036-finalizer

Change-Id: Ibfd8542fb9893f8ce05173ac6aa3cb4940cd4330