Properly handle objectClass attribute

Author: jbachorik

dd-java-agent/agent-profiling/profiling-otel/src/main/java/com/datadog/profiling/otel/JfrToOtlpConverter.java

@@ -416,7 +416,7 @@ private void handleObjectSample(ObjectSample event, Control ctl) {
     int sampleTypeIndex = getSampleTypeAttributeIndex("alloc");
     String className = null;
     try {
-      className = event.objectClass();
+      className = event.objectClass().name();
     } catch (Exception ignored) {
       // objectClass field doesn't exist in this JFR event - skip it
     }

dd-java-agent/agent-profiling/profiling-otel/src/main/java/com/datadog/profiling/otel/jfr/ObjectSample.java

@@ -21,7 +21,7 @@ public interface ObjectSample {
   long allocationSize();
 
   @JfrField("objectClass")
-  String objectClass();
+  JfrClass objectClass();
 
   @JfrField("size")
   long size();