REFACTOR: use rest serializer for tag-info categories

But the "synonyms" can't use the TagSerializer yet. We still have some
code from the discourse-tagging plugin that uses "text" instead of
"name", "count" instead of "topic_count", etc. We should make the js
consistent with the TagSerializer and then stop using tag_counts_json.

test/javascripts/acceptance/tags-test.js.es6

@@ -217,6 +217,7 @@ acceptance("Tag info", {
 
     server.get("/tags/planters/info", () => {
       return helper.response({
+        __rest_serializer: "1",
         tag_info: {
           id: 12,
           name: "planters",