Pull Request for Issue # .

Summary of Changes

• Remove the webcomponentsjs polyfills
• Add a tweeked version of those polyfills (right now they live under my username but you're free to fork that repo under the Joomla organization)
• Split the logic for the webcomponents polyfills and the web components loader in the core.js
• Add another file for the webcomponents polyfills. This file is read and put as inline script (few bytes) just before the body close tag.
• The webcomponents loader inserts scripts with type="module" for ES2015+ files or with an attribute nomodule for the old ES5 files. The sniffing is done in the browser
• Patches media manager with all the missing polyfills. Media manager also relies on webcomponents polyfill (we use custom elements in there as well)
• Patches the edit view for the files in the media manager component. Again webcomponents is the base here as well.

The interesting part

With this PR Joomla gets a proper way to serve ES2015+ code. Also, that code IS expected to be a module. The biggest change tho is that these files are lazily loaded, following the well established best practices. The way this is done is totally B/C.
If this in principal get's the green light, eg Production team decides that J4 should do things according to the well established best practices then I would suggest that most scripts should follow this pattern (now you might understand why I was always screaming to convert everything to Custom Elements). Let's move forward, ES6 is already 4 years old...

Testing Instructions

npm i and check the backend and the media manager (especially with IE11)

All Custom elements (the ES2015+ version) are modules now:

Documentation Changes Required

Enjoy!