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

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