Add YGErrata Enum (#1256)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1256

X-link: https://github.com/facebook/react-native/pull/37076

This adds a `YGErrata` bitset enum matching the API and guarantees described in https://github.com/facebook/yoga/issues/1247.

It is hooked up in later diffs. There are a couple of `YGExperimentalFeature` values that belong here, but keeping the current options means that the default `YGErrataNone` corresponds to existing default behavior, letting us stage the series of changes as:
1. Implement errata API
2. Update internal Yoga users we want to de-risk to `YGErrataClassic` or `YGErrataAll` (if setting `UseLegacyStretchBehaviour`)
3. Add new errata, changing Yoga defaults to be conformant, while letting internal apps opt into compatibility modes pending experimentation.

I also added a macro to let C++ users of Yoga perform bitwise operations on the enum without casting (already available for C users).

Reviewed By: rshest

Differential Revision: D45254098

fbshipit-source-id: d4b61271a8018f548f2d9d8c953db4b121a502d1

yoga/YGEnums.cpp

@@ -87,6 +87,20 @@ const char* YGEdgeToString(const YGEdge value) {
   return "unknown";
 }
 
+const char* YGErrataToString(const YGErrata value) {
+  switch (value) {
+    case YGErrataNone:
+      return "none";
+    case YGErrataStretchFlexBasis:
+      return "stretch-flex-basis";
+    case YGErrataAll:
+      return "all";
+    case YGErrataClassic:
+      return "classic";
+  }
+  return "unknown";
+}
+
 const char* YGExperimentalFeatureToString(const YGExperimentalFeature value) {
   switch (value) {
     case YGExperimentalFeatureWebFlexBasis: