Simplify name verification in ClassLoaderContext.

Do not go through OatFile::ResolveRelativeEncodedDexLocation
to avoid unnecessary handling of multi-dex suffix. That was
broken anyway because `abs_dex_location` is not expected to
be a multi-dex location as demonstrated by an additional
test which would have previously failed.

Test: Improved test in class_loader_context_test.
Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing

(cherry picked from commit 36ec598a4d887746291d003c97c2cb28b5987768)

 Bug: 147478491

Change-Id: I85405ed0cab3bde4fc8bd7fb3c0913d5bc41c62c