SPR-8020 Support UriComponentsBuilder as a controller method argument.

The UriComponentsBuilder instance passed into the method is initialized
with current request information including host, scheme, port, context
path, and the servlet mapping's literal part.

Also added shortcut methods to buildAndExpand in UriComponentsBuilder.

spring-framework-reference/src/mvc.xml

@@ -1199,6 +1199,13 @@ public class RelativePathUriTemplateController {
               indicated by the <classname>@SessionAttributes</classname>
               annotation at the handler type level.</para>
             </listitem>
+            
+            <listitem>
+              <para><classname>org.springframework.web.util.UriComponentsBuilder</classname>
+              a builder for preparing a URL relative to the current request's 
+              host, port, scheme, context path, and the literal part of the 
+              servlet mapping.</para>
+            </listitem>
           </itemizedlist></para>
 
         <para>The <interfacename>Errors</interfacename> or