Add get_class_loader_class_descriptors JVMTI extension method

This adds a new JVMTI extension:
com.android.art.class.get_class_loader_class_descriptors. This will
enumerate all of the classes known to be loadable with a given
class-loader as the defining class loader. The function gets this by
looking at all dex-files associated with the given class-loader.

Bug: 73504235
Test: ./test.py --host -j50
Change-Id: Ie54223cd40109056396ba609f92b6c02d81dd4ab