RN-only build flag

Summary: Previously I had created a RN build, locally, with a few minor differences. That had to be reverted. Instead of reverting and re-applying changes, I'm introducing a flag that can be used in the interim to produce the RN-only builds.

Reviewed By: LukeDefeo

Differential Revision: D50555055

fbshipit-source-id: edface9a1587fb51e54eebe73724032baf985c83

desktop/flipper-server-core/src/utils/environmentInfo.tsx

@@ -39,6 +39,10 @@ export async function getEnvironmentInfo(
     process.env.FLIPPER_FORCE_VERSION ??
     (isProduction ? packageJson.version : '0.0.0');
 
+  if (packageJson.reactNativeOnly) {
+    process.env.FLIPPER_REACT_NATIVE_ONLY = 'true';
+  }
+
   return {
     processId: process.pid,
     isProduction,