ART: Add GetClassFields support

Add GetClassFields support. Add a test.

Bug: 31684578
Test: m test-art-host-run-test-912-classes
Change-Id: Id7509ef10ec9c19b54b7db8637729556b91273e5
diff --git a/runtime/openjdkjvmti/ti_class.h b/runtime/openjdkjvmti/ti_class.h
index 63c9a87..34edb16 100644
--- a/runtime/openjdkjvmti/ti_class.h
+++ b/runtime/openjdkjvmti/ti_class.h
@@ -39,6 +39,11 @@
 
 class ClassUtil {
  public:
+  static jvmtiError GetClassFields(jvmtiEnv* env,
+                                   jclass klass,
+                                   jint* field_count_ptr,
+                                   jfieldID** fields_ptr);
+
   static jvmtiError GetClassSignature(jvmtiEnv* env,
                                       jclass klass,
                                       char** signature_ptr,