Extract polyfill loading into single module (#3421)

app/javascript/packs/application.js

@@ -1,32 +1,6 @@
 import main from '../mastodon/main';
+import loadPolyfills from '../mastodon/load_polyfills';
 
-const needsBasePolyfills = !(
-  window.Intl &&
-  Object.assign &&
-  Number.isNaN &&
-  window.Symbol &&
-  Array.prototype.includes
-);
-
-const needsExtraPolyfills = !(
-  window.IntersectionObserver &&
-  window.requestIdleCallback
-);
-
-// Latest version of Firefox and Safari do not have IntersectionObserver.
-// Edge does not have requestIdleCallback.
-// This avoids shipping them all the polyfills.
-if (needsBasePolyfills) {
-  Promise.all([
-    import(/* webpackChunkName: "base_polyfills" */ '../mastodon/base_polyfills'),
-    import(/* webpackChunkName: "extra_polyfills" */ '../mastodon/extra_polyfills'),
-  ]).then(main).catch(e => {
-    console.error(e); // eslint-disable-line no-console
-  });
-} else if (needsExtraPolyfills) {
-  import(/* webpackChunkName: "extra_polyfills" */ '../mastodon/extra_polyfills').then(main).catch(e => {
-    console.error(e); // eslint-disable-line no-console
-  });
-} else {
-  main();
-}
+loadPolyfills().then(main).catch(e => {
+  console.error(e); // eslint-disable-line no-console
+});