override settings for @babel/preset-env and regenerator.

Created by: heygrady

https://github.com/facebook/create-react-app/issues/5216

Adds a few new options for babel-preset-react-app. This is useful for cases where you want to customize your build targets, like building for node. This is required for adding server-side rendering to a forked/ejected react-scripts project.

• presetEnv - defaults to undefined. Used to override the default values for development and prod. Can be any valid options for @babel/present-env
• presetEnvTest - defaults to undefined. Used to override the default values for test. Can be any valid options for @babel/present-env
• regenerator - defaults to true, set to false in cases where your targets all support generators natively (like for a node target)

Usage:

Compare to webpack.config.prod.js application bundle

presets: [
  [
    require.resolve('babel-preset-react-app'),
    {
      presetEnv: {
        modules: 'cjs',
        targets: { node: 'current' },
      },
      regenerator: false,
    },
  ],
],

Compare to webpack.config.prod.js dependency bundle

presets: [
  [
    require.resolve('babel-preset-react-app/dependencies'),
    {
      helpers: true,
      presetEnv: {
        modules: 'cjs',
        targets: { node: 'current' },
      },
      regenerator: false,
    },
  ],
],