Align with Servlet 6.0 and introduce support for Jakarta WebSocket 2.1

Includes corresponding build upgrade to Tomcat 10.1.1 and Undertow 2.3.0
(while retaining runtime compatibility with Tomcat 10.0 and Undertow 2.2)

Closes gh-29435
Closes gh-29436

spring-webmvc/src/main/java/org/springframework/web/servlet/function/DefaultServerRequest.java

@@ -507,12 +507,6 @@ class DefaultServerRequest implements ServerRequest {
 			this.status = sc;
 		}
 
-		@Override
-		@Deprecated
-		public void setStatus(int sc, String sm) {
-			this.status = sc;
-		}
-
 		@Override
 		public int getStatus() {
 			return this.status;
@@ -553,18 +547,6 @@ class DefaultServerRequest implements ServerRequest {
 			throw new UnsupportedOperationException();
 		}
 
-		@Override
-		@Deprecated
-		public String encodeUrl(String url) {
-			throw new UnsupportedOperationException();
-		}
-
-		@Override
-		@Deprecated
-		public String encodeRedirectUrl(String url) {
-			throw new UnsupportedOperationException();
-		}
-
 		@Override
 		public void sendError(int sc, String msg) throws IOException {
 			throw new UnsupportedOperationException();

spring-webmvc/src/test/java/org/springframework/web/servlet/DispatcherServletTests.java

@@ -98,6 +98,7 @@ public class DispatcherServletTests {
 		complexConfig.addInitParameter("publishContext", "false");
 		complexConfig.addInitParameter("class", "notWritable");
 		complexConfig.addInitParameter("unknownParam", "someValue");
+		complexConfig.addInitParameter("jakarta.servlet.http.legacyDoHead", "true");
 
 		simpleDispatcherServlet = new DispatcherServlet();
 		simpleDispatcherServlet.setContextClass(SimpleWebApplicationContext.class);

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/AbstractServletHandlerMethodTests.java

@@ -110,7 +110,9 @@ public abstract class AbstractServletHandlerMethodTests {
 			}
 		};
 
-		servlet.init(new MockServletConfig());
+		MockServletConfig config = new MockServletConfig();
+		config.addInitParameter("jakarta.servlet.http.legacyDoHead", "true");
+		servlet.init(config);
 
 		return wac;
 	}