Add StanzaView.hasExtension(Class<? extends ExtensionElement>)

smack-core/src/main/java/org/jivesoftware/smack/packet/StanzaView.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2019 Florian Schmaus
+ * Copyright 2019-2020 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -67,6 +67,10 @@ public interface StanzaView extends XmlLangElement {
         return getExtension(qname) != null;
     }
 
+    default boolean hasExtension(Class<? extends ExtensionElement> extensionElementClass) {
+        return getExtension(extensionElementClass) != null;
+    }
+
     /**
      * Check if a extension element with the given namespace exists.
      *