Fix SpringUrl Velocity macro URI encoding

Prior to this commit, the springUrl Velocity macro would only prepend
the context to the given URL; this means that the
ServletHttpResponse.encodeUri method is not called and neither the
ResourceUrlProvider.

This commit changes this macro to use RequestContext.getContextUrl which
prepends the context and encodes the URI.

Issue: SPR-14027
Cherry-picked from 0a56667093

spring-webmvc/src/main/resources/org/springframework/web/servlet/view/velocity/spring.vm

@@ -55,7 +55,7 @@
  * Takes a relative URL and makes it absolute from the server root by
  * adding the context root for the web application.
  *#
-#macro( springUrl $relativeUrl )$springMacroRequestContext.getContextPath()${relativeUrl}#end
+#macro( springUrl $relativeUrl )$springMacroRequestContext.getContextUrl(${relativeUrl})#end
 
 #**
  * springBind