Reference inline comments.

As described in https://github.com/less/less.js/issues/2675 in-value comments are not preserved in referenced rules.

This patch adds reference marking to nodes below rules and expressions if markReferenced is available.

test/less/import/import-reference.less

@@ -37,7 +37,7 @@
 
 .zz {
   .y {
-    pulled-in: yes;
+    pulled-in: yes /* inline comment survives */;
   }
   /* comment pulled in */
 }