Add static factory methods to WebClientAdapter

Ideally one would pass WebClient directly to HttpServiceProxyFactory,
but two need to remain decoupled. This commit adds static, shortcut
methods to WebClientAdapter to create an HttpServiceProxyFactory, thus
eliminating the step to wrap the WebClient.

spring-web/src/main/java/org/springframework/web/service/invoker/HttpServiceProxyFactory.java

@@ -50,6 +50,7 @@ import org.springframework.web.service.annotation.HttpExchange;
  *
  * @author Rossen Stoyanchev
  * @since 6.0
+ * @see org.springframework.web.reactive.function.client.support.WebClientAdapter
  */
 public final class HttpServiceProxyFactory implements InitializingBean, EmbeddedValueResolverAware {
 
@@ -75,6 +76,7 @@ public final class HttpServiceProxyFactory implements InitializingBean, Embedded
 	/**
 	 * Create an instance with the underlying HTTP client to use.
 	 * @param clientAdapter an adapter for the client
+	 * @see org.springframework.web.reactive.function.client.support.WebClientAdapter#createHttpServiceProxyFactory(org.springframework.web.reactive.function.client.WebClient)
 	 */
 	public HttpServiceProxyFactory(HttpClientAdapter clientAdapter) {
 		Assert.notNull(clientAdapter, "HttpClientAdapter is required");