Rename root file from js to ts, improve platform splitting (#11012)

index.ts

@@ -0,0 +1,18 @@
+import 'react-native-gesture-handler' // must be first
+import '#/platform/polyfills'
+
+import {LogBox} from 'react-native'
+import {registerRootComponent} from 'expo'
+
+import App from '#/App'
+
+if (process.env.NODE_ENV === 'test') {
+  LogBox.ignoreAllLogs() // suppress all logs in tests
+} else {
+  LogBox.ignoreLogs(['Require cycle:']) // suppress require-cycle warnings, it's fine
+}
+
+// registerRootComponent calls AppRegistry.registerComponent('main', () => App);
+// It also ensures that whether you load the app in Expo Go or in a native build,
+// the environment is set up appropriately
+registerRootComponent(App)