XWIKI-21773: Admin section: make the WYSIWYG section pass webstandard…

… tests

* Replaced the hard coded number value with a more robust computed one.

xwiki-platform-core/xwiki-platform-ckeditor/xwiki-platform-ckeditor-ui/src/main/resources/CKEditor/VelocityMacros.xml

@@ -218,7 +218,7 @@
 
 #macro (displayCKEditorConfigProperty $configDoc $propName $action)
   <dt>
-    <label for="CKEditor.ConfigClass_0_${propName}">$configDoc.displayPrettyName($propName)</label>
+    <label for="CKEditor.ConfigClass_$escapetool.xml($configDoc.getObject("CKEditor.ConfigClass").getNumber())_${propName}">$configDoc.displayPrettyName($propName)</label>
     <span class="xHint">$escapetool.xml($services.localization.render("CKEditor.ConfigClass_${propName}.hint"))</span>
   </dt>
   <dd>#displayCKEditorConfigPropertyValue($configDoc $propName $action)</dd>