ART: Add GetClassSignature

Add support to retrieve the signature of a JNI class.

Add a test.

Bug: 31684578
Test: m test-art-host-run-test-912-classes
Change-Id: I1cf946996f9089cb5d41e93b4f1064193e9d6350
diff --git a/test/ti-agent/common_load.cc b/test/ti-agent/common_load.cc
index 7faf700..4db953c 100644
--- a/test/ti-agent/common_load.cc
+++ b/test/ti-agent/common_load.cc
@@ -35,6 +35,7 @@
 #include "909-attach-agent/attach.h"
 #include "910-methods/methods.h"
 #include "911-get-stack-trace/stack_trace.h"
+#include "912-classes/classes.h"
 
 namespace art {
 
@@ -62,6 +63,7 @@
   { "909-attach-agent", nullptr, Test909AttachAgent::OnAttach },
   { "910-methods", Test910Methods::OnLoad, nullptr },
   { "911-get-stack-trace", Test911GetStackTrace::OnLoad, nullptr },
+  { "912-classes", Test912Classes::OnLoad, nullptr },
 };
 
 static AgentLib* FindAgent(char* name) {