[LOCAL] reintroduce generated codegen files

Author: kelset

.gitignore

@@ -105,7 +105,6 @@ package-lock.json
 !/packages/rn-tester/Pods/__offline_mirrors__
 
 # react-native-codegen
-/React/FBReactNativeSpec/FBReactNativeSpec
 /packages/react-native-codegen/lib
 /ReactCommon/react/renderer/components/rncore/
 /packages/rn-tester/NativeModuleExample/ScreenshotManagerSpec*