8256167: Convert JDK use of Reference::get to Reference::refersTo

Reviewed-by: sspitsyn, shade, dfuchs, alanb, kbarrett

src/java.base/share/classes/java/lang/Thread.java

@@ -2044,9 +2044,9 @@ public class Thread implements Runnable {
                 return true;
 
             if (obj instanceof WeakClassKey) {
-                Object referent = get();
+                Class<?> referent = get();
                 return (referent != null) &&
-                       (referent == ((WeakClassKey) obj).get());
+                        (((WeakClassKey) obj).refersTo(referent));
             } else {
                 return false;
             }