That package was missed in gh-4865 as it only broke browsers needing the
polyfill which is just IE at the moment. Thus, it broke Core tests in IE only.
Ref gh-4865
Closes gh-4870
So far, we've been testing that jQuery element iteration works with polyfilled
Symbol & transpiled for-of via a Node test with jsdom with the Symbol global
removed. Unfortunately, jsdom now requires Symbol to be present for its internal
functionality so such a test is no longer possible. Instead, it's been migrated
to an iframe test with transpiled JavaScript.
This PR also enables us to use ECMAScript 2017 or newer in Node.js code.
Closes gh-4305