Add support for WebSocket Protocol Extensions

This commits adds simple, overridable WebSocket Extension
filtering during the handshake phase and adds that
information in the WebSocket session.

The actual WebSocket Extension negotiation happens
within the server implementation (Glassfish, Jetty, Tomcat...),
so one can only remove requested extensions from
the list provided by the WebSocket client.

See RFC6455 Section 9.

Issue: SPR-10843

spring-messaging/src/main/java/org/springframework/messaging/handler/websocket/SubProtocolHandler.java

@@ -69,7 +69,7 @@ public interface SubProtocolHandler {
 	/**
 	 * Resolve the session id from the given message or return {@code null}.
 	 *
-	 * @param the message to resolve the session id from
+	 * @param message the message to resolve the session id from
 	 */
 	String resolveSessionId(Message<?> message);