Fix standalone package build for unity plugins

Summary: Fixed error on building standalone packages for "unity" apps. The error was because "immer" imports were not transformed to use "immer" from Flipper bundle.

Reviewed By: passy

Differential Revision: D22357571

fbshipit-source-id: 590321f36208c9ed02d56d2c0c085c7cd1878018

desktop/babel-transformer/src/replace-flipper-requires.ts

@@ -21,6 +21,7 @@ const requireReplacements: any = {
   react: 'global.React',
   'react-dom': 'global.ReactDOM',
   adbkit: 'global.adbkit',
+  immer: 'global.Immer',
 };
 
 export function tryReplaceFlipperRequire(path: NodePath<CallExpression>) {