Provide a way to add the '.js' file extension to the end of module specifiers #16577
Description
In order to use es6 modules in the browser, you need a .js file extension. However output doesn't add it.
In ts:
import { ModalBackground } from './ModalBackground';
In ES2015 output:
import { ModalBackground } from './ModalBackground';
Ideally I would like this to be output
import { ModalBackground } from './ModalBackground.js';
That way I can use the output in Chrome 51
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Webpack boilerplate</title>
<script type="module" src="index.js"></script>
</head>
<body></body>
</html>
Related to #13422