Launch early, even if not ready

Summary:
Flipper Launcher downloads, unpacks, launches Flipper, and closes itself.

This is fine except for the fact that Flipper may be initiating and thus there's a gap of a few seconds until engineers see the main Flipper UI.

This change improves this by launching earlier, even if just showing a loading page until Flipper is actually ready.

Reviewed By: passy, aigoncharov

Differential Revision: D48824479

fbshipit-source-id: aa6147a09f313d80592c9b08d089660ba73773a4

desktop/flipper-server/src/index.tsx

@@ -215,6 +215,9 @@ async function start() {
     `[flipper-server][bootstrap] HTTP server started (${httpServerStartedMS} ms)`,
   );
 
+  // At this point, the HTTP server is ready and listening.
+  launch();
+
   const flipperServer = await startFlipperServer(
     rootPath,
     staticPath,
@@ -342,7 +345,7 @@ process.on('unhandledRejection', (reason, promise) => {
 });
 
 start()
-  .then(launch)
+  .then(() => {})
   .catch((e) => {
     console.error(chalk.red('Server startup error: '), e);
     process.exit(1);