DEV: adds a `stringToHTML` helper to be used in tests (#8424)

This will replace the need for jquery: `$(string)`

test/javascripts/helpers/html-helper.js.es6

@@ -0,0 +1,5 @@
+export function stringToHTML(string) {
+  const parser = new DOMParser();
+  const doc = parser.parseFromString(string, "text/html");
+  return doc.body.firstChild;
+}