Refine VarHandle::GetMethodTypeMatchForAccessMode()

Treat assignable types as exact to broaden cases in the runtime that
take the faster path. Also treat parameters of type j.l.Void as
assignable since this means the parameter value is null.

Remove unused VarHandle::IsInvokerMethodTypeCompatible().

Bug: 65872996
Test: art/test.py --host -r -t 712
Test: m test-art-host-gtest
Change-Id: I0aea10b53d03a1a13ff23dfedaeb0d1c75c3f1ff
4 files changed