FIX: Tests were broken in Firefox (#12456)

There are a lot of little fixes to tests here, but the biggest issue was
too much recursion because we kept replacing the helpers over and over
again. I assume Chrome has tail recursion or something to speed this up
but Firefox hated it.

Otherwise, we can't rely on the order of attributes in rendered HTML so
I simplified most of those tests to just look for key strings in the
HTML that are rendered.

app/assets/javascripts/discourse-common/addon/lib/raw-handlebars-helpers.js

@@ -8,6 +8,10 @@ export function registerRawHelpers(hbs, handlebarsClass) {
   if (!hbs.helpers) {
     hbs.helpers = Object.create(handlebarsClass.helpers);
   }
+  if (hbs.__helpers_registered) {
+    return;
+  }
+  hbs.__helpers_registered = true;
 
   hbs.helpers["get"] = function (context, options) {
     if (!context || !options.contexts) {