Encapsulate arrays of YGValue within YGStyle

Summary:
@public

Enforce more encapsulation of arrays of `YGValue` in `YGSty;e`.
This will allow us to use `CompactValue` in `YGStyle` while (mostly) retaining API compatibility.

Reviewed By: SidharthGuglani

Differential Revision: D13452042

fbshipit-source-id: 382b1c7245c4bea4280126ab1413e7e931b62eaa

yoga/YGValue.h

@@ -46,6 +46,8 @@ inline bool operator==(const YGValue& lhs, const YGValue& rhs) {
     case YGUnitPercent:
       return lhs.value == rhs.value;
   }
+
+  return false;
 }
 
 inline bool operator!=(const YGValue& lhs, const YGValue& rhs) {