8302791: Add specific ClassLoader object to Proxy IllegalArgumentException message

Reviewed-by: alanb, mchung

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

@@ -407,6 +407,11 @@ public abstract class ClassLoader {
         return nid;
     }
 
+    // Returns nameAndId string for exception message printing
+    String nameAndId() {
+        return nameAndId;
+    }
+
     /**
      * Creates a new class loader of the specified name and using the
      * specified parent class loader for delegation.