Add ClientResponse::createError

This commit introduces ClientResponse::createError, returning
a Mono that terminates with a WebClientException.

Closes gh-27637

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/ClientResponse.java

@@ -181,6 +181,18 @@ public interface ClientResponse {
 	 */
 	Mono<WebClientResponseException> createException();
 
+	/**
+	 * Create a {@code Mono} that terminates with a
+	 * {@link WebClientResponseException}, containing the response status,
+	 * headers, body, and the originating request.
+	 * @param <T> the reified type
+	 * @return a {@code Mono} that fails with a
+	 * {@link WebClientResponseException}.
+	 * @see #createException()
+	 * @since 6.0
+	 */
+	<T> Mono<T> createError();
+
 	/**
 	 * Return a log message prefix to use to correlate messages for this exchange.
 	 * <p>The prefix is based on {@linkplain ClientRequest#logPrefix()}, which

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientResponse.java

@@ -223,6 +223,11 @@ class DefaultClientResponse implements ClientResponse {
 				});
 	}
 
+	@Override
+	public <T> Mono<T> createError() {
+		return createException().flatMap(Mono::error);
+	}
+
 	@Override
 	public String logPrefix() {
 		return this.logPrefix;

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/support/ClientResponseWrapper.java

@@ -153,6 +153,11 @@ public class ClientResponseWrapper implements ClientResponse {
 		return this.delegate.createException();
 	}
 
+	@Override
+	public <T> Mono<T> createError() {
+		return this.delegate.createError();
+	}
+
 	@Override
 	public String logPrefix() {
 		return this.delegate.logPrefix();