ART: Add GetClassLoaderClasses

Add support for GetClassLoaderClasses, extracting all classes a
given classloader initiated. Add test.

Bug: 31684578
Test: m test-art-host-run-test-912-classes
Change-Id: I0aba27fb1674baf1263c0a19dc2dcce7af013760
diff --git a/runtime/openjdkjvmti/OpenjdkJvmTi.cc b/runtime/openjdkjvmti/OpenjdkJvmTi.cc
index 8674e6c..53ff8ea 100644
--- a/runtime/openjdkjvmti/OpenjdkJvmTi.cc
+++ b/runtime/openjdkjvmti/OpenjdkJvmTi.cc
@@ -535,7 +535,7 @@
                                           jobject initiating_loader,
                                           jint* class_count_ptr,
                                           jclass** classes_ptr) {
-    return ERR(NOT_IMPLEMENTED);
+    return ClassUtil::GetClassLoaderClasses(env, initiating_loader, class_count_ptr, classes_ptr);
   }
 
   static jvmtiError GetClassSignature(jvmtiEnv* env,