ART: Take classloader into account for AttachAgent

Take a classloader into account for attaching an agent, if given.
This will use the library path from the classloader to find the
agent library.

Switch to libnativeloader to do the actual loading.

Bug: 70901841
Test: m test-art-host
Change-Id: I59ec55178792bc738fb06e0299522e207dd4a784
8 files changed