App bundle for server

Summary:
This bundles up the Flipper Server in a Mac App Bundle which is identically in shape to a regular Desktop bundle. That means we can swap them out transparently without having to keep the layout in sync with Flipper Launcher.

It bundles nodeJS binary which we can later also provide for aarch64.

Reviewed By: aigoncharov

Differential Revision: D36140809

fbshipit-source-id: fb3410626ab172ce0da48f1a4a1489da68450369

desktop/scripts/build-utils.tsx

@@ -368,11 +368,13 @@ export async function compileMain() {
     die(err);
   }
 }
-export function buildFolder(): Promise<string> {
+export function buildFolder(
+  prefix: string = 'flipper-build-',
+): Promise<string> {
   // eslint-disable-next-line no-console
   console.log('Creating build directory');
   return new Promise<string>((resolve, reject) => {
-    tmp.dir({prefix: 'flipper-build-'}, (err, buildFolder) => {
+    tmp.dir({prefix}, (err, buildFolder) => {
       if (err) {
         reject(err);
       } else {