Add smack-websocket-java11

This also lifts a bunch of logic from smack-websocket-okhttp into
smack-websocket. Furthermore, the following subprojects require now
Java 11:
- smack-integration-test
- smack-omemo-signal-integration-test
- smack-repl
- smack-websocket-java11

Related tracking issue: SMACK-835

smack-core/src/main/java/org/jivesoftware/smack/c2s/XmppClientToServerTransport.java

@@ -54,8 +54,6 @@ public abstract class XmppClientToServerTransport {
 
     public abstract SSLSession getSslSession();
 
-    public abstract boolean isConnected();
-
     public boolean isTransportSecured() {
         return getSslSession() != null;
     }

smack-core/src/main/java/org/jivesoftware/smack/util/rce/RemoteConnectionEndpoint.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2020 Florian Schmaus
+ * Copyright 2020-2021 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,6 +32,10 @@ public interface RemoteConnectionEndpoint {
 
     String getDescription();
 
+    default String getRawString() {
+        return toString();
+    }
+
     class InetSocketAddressCoupling<RCE extends RemoteConnectionEndpoint> {
         private final RCE connectionEndpoint;
         private final InetSocketAddress inetSocketAddress;