Add support for node_modules to be included in babel

[adambutler]

I've found dependencies that are ES6 fail during UglifyJs due to not first being handled by babel:

For example, my code has:

import { Foundation } from 'foundation-sites/js/foundation.core';
import { Reveal } from 'foundation-sites/js/foundation.reveal';
import { Tabs } from 'foundation-sites/js/foundation.tabs'

When I run:

$ rm -Rf public/packs
$ NODE_ENV=production RAILS_ENV=production rails webpacker:compile --trace

I get the following error:

ERROR in application-37763722852138e61493.js from UglifyJs
Unexpected character '`' [./node_modules/foundation-sites/js/foundation.util.core.js:24,0][application-37763722852138e61493.js:11323,124]

ERROR in Modals-8541f74f3cf2b70f4a0f.js from UglifyJs
Unexpected token: name (matchMedia) [./node_modules/foundation-sites/js/foundation.util.mediaQuery.js:21,0][Modals-8541f74f3cf2b70f4a0f.js:102,4]

ERROR in TabbedExamples-b873f916d365855bfd5d.js from UglifyJs
Unexpected character '`' [./node_modules/foundation-sites/js/foundation.util.core.js:24,0][TabbedExamples-b873f916d365855bfd5d.js:100,124]

This change adds the ability to include node_modules to be compiled by babel. It defaults to the current behaviour, which I'm not entirely sure is correct anyway.

Related: #395
Possibly related: #746

Copying in @dhh @gauravtiwari who have both touched package/loaders/babel.js.

[gauravtiwari]

@adambutler Thanks for this but if you want to include node_modules in your app, you can update the loader yourself in your environment.js

// config/webpack/environment.js
const { environment } = require('@rails/webpacker')

// Update an option directly
const babelLoader = environment.loaders.get('babel')
babelLoader.exclude = []

module.exports = environment