Upgrade to Tomcat 11.0

This commit upgrades the baseline to Tomcat 11.0 and adapts to the
following behavior changes in Tomcat:

* the MimeHeaders#clear method has been removed
* expired cookies do not set "Max-Age=0" anymore
* responses to HEAD requests do not write the "Content-Length" header
  anymore.

Closes gh-33916

framework-platform/framework-platform.gradle

@@ -103,10 +103,10 @@ dependencies {
 		api("org.apache.httpcomponents.client5:httpclient5:5.4.1")
 		api("org.apache.httpcomponents.core5:httpcore5-reactive:5.3.1")
 		api("org.apache.poi:poi-ooxml:5.2.5")
-		api("org.apache.tomcat.embed:tomcat-embed-core:10.1.28")
-		api("org.apache.tomcat.embed:tomcat-embed-websocket:10.1.28")
-		api("org.apache.tomcat:tomcat-util:10.1.28")
-		api("org.apache.tomcat:tomcat-websocket:10.1.28")
+		api("org.apache.tomcat.embed:tomcat-embed-core:11.0.1")
+		api("org.apache.tomcat.embed:tomcat-embed-websocket:11.0.1")
+		api("org.apache.tomcat:tomcat-util:11.0.1")
+		api("org.apache.tomcat:tomcat-websocket:11.0.1")
 		api("org.aspectj:aspectjrt:1.9.22.1")
 		api("org.aspectj:aspectjtools:1.9.22.1")
 		api("org.aspectj:aspectjweaver:1.9.22.1")

spring-web/src/main/java/org/springframework/http/server/reactive/TomcatHeadersAdapter.java

@@ -161,10 +161,11 @@ class TomcatHeadersAdapter implements MultiValueMap<String, String> {
 		map.forEach(this::put);
 	}
 
-	@SuppressWarnings("deprecation")  // on Tomcat 10.1.16+
 	@Override
 	public void clear() {
-		this.headers.clear();
+		for (int i = 0 ; i < this.headers.size(); i++) {
+			this.headers.removeHeader(i);
+		}
 	}
 
 	@Override

spring-web/src/test/java/org/springframework/web/server/session/WebSessionIntegrationTests.java

@@ -141,7 +141,7 @@ class WebSessionIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 		assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
 		String value = response.getHeaders().getFirst("Set-Cookie");
 		assertThat(value).isNotNull();
-		assertThat(value).as("Actual value: " + value).contains("Max-Age=0");
+		assertThat(value).as("Actual value: " + value).containsAnyOf("Expires=Thu, 01 Jan 1970", "Max-Age=0");
 	}
 
 	@ParameterizedHttpServerTest
@@ -189,7 +189,7 @@ class WebSessionIntegrationTests extends AbstractHttpHandlerIntegrationTests {
 		assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
 		String value = response.getHeaders().getFirst("Set-Cookie");
 		assertThat(value).isNotNull();
-		assertThat(value).as("Actual value: " + value).contains("Max-Age=0");
+		assertThat(value).as("Actual value: " + value).containsAnyOf("Expires=Thu, 01 Jan 1970", "Max-Age=0");
 	}
 
 	private String extractSessionId(HttpHeaders headers) {

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/RequestMappingIntegrationTests.java

@@ -93,7 +93,6 @@ class RequestMappingIntegrationTests extends AbstractRequestMappingIntegrationTe
 		HttpHeaders headers = getRestTemplate().headForHeaders(url);
 		String contentType = headers.getFirst("Content-Type");
 		assertThat(contentType).isNotNull();
-		assertThat(headers.getContentLength()).isEqualTo(3);
 	}
 
 	@ParameterizedHttpServerTest