Backpackify

[matthewdavidson]

This PR upgrades backpack-react-scripts from CRA 1.X to CRA 2.X. When reviewing, it's useful to compare it to the diff in #40 which contains all the changes made to CRA 1.X for backpack-react-scripts.

Breaking changes:

See full list, the biggest being:

1. Polyfills are no longer shipped by default.
2. Vendor/common chunks enabled by default
   This has been reversed so that they are now opt in via enableAutomaticChunking
3. The asset-manifest.json is useless now
   - asset-manifest.json generated by CRA2 is not useful facebook/create-react-app#5513
   - Static keys for vendor bundle in asset-manifest.json facebook/create-react-app#5225
   Worked around this by setting name in splitChunks: { chunks: 'all', name: false, }, to true.
   Also added css.html and js.html fragments to output folder to encapsulate script order.

Here is a list of things to test:

• CSS modules
• CSS modules class name collisions
• SSR
• lodash leaking to global scope
• jsonpFunction
• sassFunctions
• npm run lint
• "backpack-react-scripts" config:
  • crossOriginLoading
  • babelIncludePrefixes
  • disablePolyfills no longer required
  • amdExcludes
  • externals
  • ssrExternals
  • cssModules

[matthewdavidson]

Currently, the build is failing due to the following:

./src/index.js
Error: [BABEL] /tmp/tmp.ITFnhIWwCi/test-app/src/index.js: Cannot find module '@babel/plugin-transform-react-jsx' (While processing: "/tmp/tmp.ITFnhIWwCi/test-app/node_modules/babel-preset-react-app/index.js$1")
    at Array.reduce (<anonymous>)

This is the exact same failure that is happening on upstream/master: https://travis-ci.org/facebook/create-react-app/builds/474283066.

Related issue: facebook#6099

[shaundon]

Suggested change

In order to benefit from the ongoing open source development of create-react-app, this fork is kept up-to-date with the upstream repo. To aid this, we have preserved the existing repo structure, including all of the source code for the other packages that live alongside [`react-scripts`](https://github.com/facebook/create-react-app/tree/master/packages/react-scripts). **We do not modify any source code outside of [`react-scripts`](https://github.com/facebook/create-react-app/tree/master/packages/react-scripts).**

In order to benefit from the ongoing open-source development of create-react-app, this fork is kept up-to-date with the upstream repo. To aid this, we have preserved the existing repo structure, including all of the source code for the other packages that live alongside [`react-scripts`](https://github.com/facebook/create-react-app/tree/master/packages/react-scripts). **We do not modify any source code outside of [`react-scripts`](https://github.com/facebook/create-react-app/tree/master/packages/react-scripts).**