ART: Improve double-JNI-load exception message

Try to print the involved classloaders. The code is suboptimal
and will not cache any intermediates, as this is an unexpected
failure - but aids in debugging application issues.

Add a test for the behavior of duplicate library loading in
separate classloaders. For ART, add a rough test for the pattern
of the error message.

Bug: 65574359
Test: m test-art-host
Test: art/test/testrunner/testrunner.py -b --host -t 004-JniTest
Change-Id: I6c6c7726a79172f39153d4a458eba4fb3e8e85b0