ART: Refactor verifier

Move implementation to internal class, only keep minimal interface
that other classes depend on public.

An internal impl::anonymous namespace and duplicate MethodVerifier
name was chosen so as to minimize the patch.

In preparation for templatization.

(cherry picked from commit fc25ae90c7f2b93ce4cd7a920afaf893c17d08cb)

Bug: 130904871
Test: mmma art
Test: m test-art-host
Merged-In: I79de01139b8fbd8b4e828bb0e58faeb8666176d5
Change-Id: I79de01139b8fbd8b4e828bb0e58faeb8666176d5