Set babel to utilize `useBuiltIns: "usage”`

Removes explict calls to core-js polyfills.
Lets babel find polyfills when needed for our target browsers.

app/assets/javascripts/commons/polyfills.js

-// ECMAScript polyfills
-import 'core-js/es/array/fill';
-import 'core-js/es/array/find';
-import 'core-js/es/array/find-index';
-import 'core-js/es/array/from';
-import 'core-js/es/array/includes';
-import 'core-js/es/number/is-integer';
-import 'core-js/es/object/assign';
-import 'core-js/es/object/values';
-import 'core-js/es/object/entries';
-import 'core-js/es/promise';
-import 'core-js/es/promise/finally';
-import 'core-js/es/string/code-point-at';
-import 'core-js/es/string/from-code-point';
-import 'core-js/es/string/includes';
-import 'core-js/es/string/starts-with';
-import 'core-js/es/string/ends-with';
-import 'core-js/es/symbol';
-import 'core-js/es/map';
-import 'core-js/es/weak-map';
-import 'core-js/modules/web.url';
-
 // Browser polyfills
 import 'formdata-polyfill';
 import './polyfills/custom_event';

app/assets/javascripts/locale/es6/ensure_single_line.js

+// co-locating ensure_single_line to satisfy static analysis while allowing Node.js to import the function with CommonJS
+
+import ensureSingleLine from '../ensure_single_line';
+
+export default ensureSingleLine;

app/assets/javascripts/locale/index.js

 import Jed from 'jed';
-import ensureSingleLine from './ensure_single_line';
+import ensureSingleLine from './es6/ensure_single_line';
 import sprintf from './sprintf';
 
 const languageCode = () => document.querySelector('html').getAttribute('lang') || 'en';

app/assets/javascripts/test_utils/index.js

-import 'core-js/es/map';
-import 'core-js/es/set';
 import { Sortable } from 'sortablejs';
 import simulateDrag from './simulate_drag';
 import simulateInput from './simulate_input';

babel.config.js

@@ -6,6 +6,8 @@ const presets = [
   [
     '@babel/preset-env',
     {
+      useBuiltIns: 'usage',
+      corejs: { version: 3, proposals: true },
       modules: false,
       targets: {
         ie: '11',
@@ -51,4 +53,4 @@ if (isJest) {
   plugins.push('babel-plugin-dynamic-import-node');
 }
 
-module.exports = { presets, plugins };
+module.exports = { presets, plugins, sourceType: 'unambiguous' };

package.json

@@ -31,7 +31,7 @@
     "webpack-prod": "NODE_OPTIONS=\"--max-old-space-size=3584\" NODE_ENV=production webpack --config config/webpack.config.js"
   },
   "dependencies": {
-    "@babel/core": "^7.6.2",
+    "@babel/core": "^7.7.5",
     "@babel/plugin-proposal-class-properties": "^7.5.5",
     "@babel/plugin-proposal-json-strings": "^7.2.0",
     "@babel/plugin-proposal-optional-chaining": "^7.7.5",
@@ -65,7 +65,7 @@
     "codesandbox-api": "^0.0.20",
     "compression-webpack-plugin": "^3.0.1",
     "copy-webpack-plugin": "^5.0.5",
-    "core-js": "^3.2.1",
+    "core-js": "^3.4.0",
     "cropper": "^2.3.0",
     "css-loader": "^1.0.0",
     "d3": "^4.13.0",

spec/frontend/locale/ensure_single_line_spec.js

-import ensureSingleLine from '~/locale/ensure_single_line';
+import ensureSingleLine from '~/locale/es6/ensure_single_line';
 
 describe('locale', () => {
   describe('ensureSingleLine', () => {