Remove import-sideffect call to init()

Summary:
Back out "Back out "[flipper] Export init function""
Original commit changeset: 93b916d472b7

The import side effect seems to cause some issues with shadowing,
so let's pull this all the way to the top and call this from HTML
as Sonar.init().

Reviewed By: danielbuechele

Differential Revision: D9849869

fbshipit-source-id: b62772ecddc59eab00251ebf19816f470d76ba82

src/init.js

@@ -62,16 +62,18 @@ const AppFrame = () => (
   </TooltipProvider>
 );
 
-// $FlowFixMe: this element exists!
-ReactDOM.render(<AppFrame />, document.getElementById('root'));
-// $FlowFixMe: service workers exist!
-navigator.serviceWorker
-  .register(
-    process.env.NODE_ENV === 'production'
-      ? path.join(__dirname, 'serviceWorker.js')
-      : './serviceWorker.js',
-  )
-  .then(r => {
-    (r.installing || r.active).postMessage({precachedIcons});
-  })
-  .catch(console.error);
+export default function init() {
+  // $FlowFixMe: this element exists!
+  ReactDOM.render(<AppFrame />, document.getElementById('root'));
+  // $FlowFixMe: service workers exist!
+  navigator.serviceWorker
+    .register(
+      process.env.NODE_ENV === 'production'
+        ? path.join(__dirname, 'serviceWorker.js')
+        : './serviceWorker.js',
+    )
+    .then(r => {
+      (r.installing || r.active).postMessage({precachedIcons});
+    })
+    .catch(console.error);
+}