Prepare Undertow 1.3.0 compatibility

Xnio 3.4.0 will introduce a new source of ByteBuffers: ByteBufferPool.
Previously this feature was offered by Pooled/Pool/ByteBufferSlicePool;
those classes are now marked as deprecated.

As of 1.3.0.Beta9, Undertow still implements the following method in its
ClientConnection interface, using those deprecated types:

    Pool<ByteBuffer> getBufferPool();

This commit prepares compatibility by suppressing warnings in order to
avoid build failures in our build. Once appropriate changes are made in
Undertow, a specific implementation with new types could be introduced.

Issue: SPR-13366

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

@@ -38,7 +38,6 @@ import org.springframework.util.SocketUtils;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.servlet.DispatcherServlet;
 
-import org.xnio.ByteBufferSlicePool;
 import org.xnio.OptionMap;
 import org.xnio.Xnio;
 
@@ -70,6 +69,7 @@ public class UndertowTestServer implements WebSocketTestServer {
 	}
 
 	@Override
+	@SuppressWarnings("deprecation")
 	public void deployConfig(WebApplicationContext wac, Filter... filters) {
 		Assert.state(this.port != -1, "setup() was never called");
 		DispatcherServletInstanceFactory servletFactory = new DispatcherServletInstanceFactory(wac);
@@ -78,7 +78,7 @@ public class UndertowTestServer implements WebSocketTestServer {
 		WebSocketDeploymentInfo info = new WebSocketDeploymentInfo();
 		try {
 			info.setWorker(Xnio.getInstance().createWorker(OptionMap.EMPTY));
-			info.setBuffers(new ByteBufferSlicePool(1024,1024));
+			info.setBuffers(new org.xnio.ByteBufferSlicePool(1024,1024));
 		}
 		catch (IOException ex) {
 			throw new IllegalStateException(ex);