C++ style enums 1/N: Generator (#1384)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1384

X-link: https://github.com/facebook/react-native/pull/39446

This adds logic to the enum generator to generate C++ style scoped enums.

This gives us a few nicities over C enums, even if both must exist:
1. We can add types and keep unsgined enums directly in bitfields
2. Style/readability
3. Avoiding implicit int conversion

Reviewed By: rozele

Differential Revision: D49267996

fbshipit-source-id: 1c41164c377b317c1fef97811c46cbc00b5a837e

yoga/YGEnums.h

@@ -6,13 +6,10 @@
  */
 
 // @generated by enums.py
-
+// clang-format off
 #pragma once
 #include <yoga/YGMacros.h>
 
-// clang-format off
-
-
 YG_EXTERN_C_BEGIN
 
 YG_ENUM_SEQ_DECL(