Pass the class loader context to dex2oat when optimizing at runtime

Until now we always passed the special shared library symbol "&" when we
called dex2oat at runtime without an explicit class path.

This CL changes that and passes the class loader context inferred from the
runtime class loaders to dex2oat. If any of the runtime class loaders is
not supported we continue to pass the special library symbol.

Bug: 38138251
Test: m test-art-host
Change-Id: Ica43ee8a3f36dab2d9ed0e634a9f6341379c8e1c