Drop IE 11 support by default (facebook#5090)

* Drop ie 11 support and move polyfills to a new package

* More useful directions for what entry point to use
facebook#5090 (comment)

* Clear up what file this polyfill goes in
facebook#5090 (comment)

* Polyfill `window`, not `global`

* Remove proxy polyfill file

Author: Timer

config/polyfills.js

@@ -82,10 +82,7 @@ module.exports = {
   devtool: 'cheap-module-source-map',
   // These are the "entry points" to our application.
   // This means they will be the "root" imports that are included in JS bundle.
-  // The first two entry points enable "hot" CSS and auto-refreshes for JS.
   entry: [
-    // We ship a few polyfills by default:
-    require.resolve('./polyfills'),
     // Include an alternative client for WebpackDevServer. A client's job is to
     // connect to WebpackDevServer by a socket and get notified about changes.
     // When you save a file, the client will either apply hot updates (in case

config/webpack.config.dev.js

@@ -100,8 +100,8 @@ module.exports = {
   // We generate sourcemaps in production. This is slow but gives good results.
   // You can exclude the *.map files from the build during deployment.
   devtool: shouldUseSourceMap ? 'source-map' : false,
-  // In production, we only want to load the polyfills and the app code.
-  entry: [require.resolve('./polyfills'), paths.appIndexJs],
+  // In production, we only want to load the app code.
+  entry: [paths.appIndexJs],
   output: {
     // The build folder.
     path: paths.appBuild,

config/webpack.config.prod.js

@@ -50,14 +50,12 @@
     "jest": "23.6.0",
     "loader-utils": "1.1.0",
     "mini-css-extract-plugin": "0.4.3",
-    "object-assign": "4.1.1",
     "optimize-css-assets-webpack-plugin": "5.0.1",
     "postcss-flexbugs-fixes": "4.1.0",
     "postcss-loader": "3.0.0",
     "postcss-preset-env": "6.0.6",
     "postcss-safe-parser": "4.0.1",
-    "promise": "8.0.2",
-    "raf": "3.4.0",
+    "react-app-polyfill": "^0.0.0",
     "react-dev-utils": "^5.0.0",
     "resolve": "1.8.1",
     "sass-loader": "7.1.0",
@@ -68,8 +66,7 @@
     "url-loader": "1.1.1",
     "webpack": "4.19.1",
     "webpack-dev-server": "3.1.9",
-    "webpack-manifest-plugin": "2.0.4",
-    "whatwg-fetch": "3.0.0"
+    "webpack-manifest-plugin": "2.0.4"
   },
   "devDependencies": {
     "react": "^16.3.2",

package.json

@@ -22,7 +22,7 @@ module.exports = (resolve, rootDir, isEjecting) => {
   // in Jest configs. We need help from somebody with Windows to determine this.
   const config = {
     collectCoverageFrom: ['src/**/*.{js,jsx}'],
-    setupFiles: [resolve('config/polyfills.js')],
+    setupFiles: ['react-app-polyfill/jsdom'],
     setupTestFrameworkScriptFile: setupTestsFile,
     testMatch: [
       '<rootDir>/src/**/__tests__/**/*.{js,jsx}',