Fix missing "os" polyfill
Fix missing "os" polyfill

Summary:
Webpack 5 no longer polyfills "os".
Force bundles to provide an empty module for "os" for browsers.

Reviewed By: antonk52

Differential Revision: D35114196

fbshipit-source-id: 82dd2dc9e15dafc595f9242cdb2f3cb1ddf07268

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper