ART: Clean up library loading

Retrieve the library path from the classloader before attempting to
load, instead of getting it passed down. This allows unifying said
loading behavior for follow-up changes.

Fix up test code to support the new required data in classloader
objects.

Bug: 70901841
Test: m test-art-host
Test: device boots
Change-Id: Iaccaeb56422877abac9f7fe6f5a17364c8adf4ca