Despite core is dropping formal support for IE in our template neither do we want to make it too hard to build frontend templates on IE. Basically in core we can use the ES6 files natively now and we also don't want to have to add IE code in this.

I believe we can use this https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md#web-standards for the es5 files which will hopefully still be ie11 compat (but not used by core but provided as a service for templates who require it). And that will polyfill nodeList.foreach removing our requirement for example to use [].slice.call() from JS as an example

This came out of this closed issue #25566