Deprecate JettyWebSocketClient in favor of StandardWebSocketClient

JettyWebSocketClient only supported on Jetty 11, to be phased out.

Closes gh-29576

spring-websocket/src/test/java/org/springframework/web/socket/AbstractWebSocketIntegrationTests.java

@@ -65,6 +65,7 @@ public abstract class AbstractWebSocketIntegrationTests {
 		upgradeStrategyConfigTypes.put(UndertowTestServer.class, UndertowUpgradeStrategyConfig.class);
 	}
 
+	@SuppressWarnings("removal")
 	static Stream<Arguments> argumentsFactory() {
 		return Stream.of(
 				arguments(named("Jetty", new JettyWebSocketTestServer()), named("Jetty", new JettyWebSocketClient())),

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/client/JettySockJsIntegrationTests.java

@@ -42,6 +42,7 @@ class JettySockJsIntegrationTests extends AbstractSockJsIntegrationTests {
 		return new JettyWebSocketTestServer();
 	}
 
+	@SuppressWarnings("removal")
 	@Override
 	protected Transport createWebSocketTransport() {
 		return new WebSocketTransport(new JettyWebSocketClient());