Move out YGValue

Summary:
@public

Creates a single header file for `YGValue`. This is in preparation of a more compact representation of `YGValue` within `YGStyle`.

Also fixes the incorrect definition of NAN.

Reviewed By: SidharthGuglani

Differential Revision: D13439602

fbshipit-source-id: 68eef2c391b6c9810f3c995b86fff7204ebe6511

yoga/Yoga.h

@@ -17,16 +17,9 @@
 #include <stdbool.h>
 #endif
 
-// Not defined in MSVC++
-#ifndef NAN
-static const unsigned long __nan[2] = {0xffffffff, 0x7fffffff};
-#define NAN (*(const float*)__nan)
-#endif
-
-#define YGUndefined NAN
-
 #include "YGEnums.h"
 #include "YGMacros.h"
+#include "YGValue.h"
 
 YG_EXTERN_C_BEGIN
 
@@ -35,25 +28,6 @@ typedef struct YGSize {
   float height;
 } YGSize;
 
-typedef struct YGValue {
-  float value;
-  YGUnit unit;
-} YGValue;
-
-extern const YGValue YGValueUndefined;
-extern const YGValue YGValueAuto;
-
-#ifdef __cplusplus
-
-YG_EXTERN_C_END
-
-extern bool operator==(const YGValue& lhs, const YGValue& rhs);
-extern bool operator!=(const YGValue& lhs, const YGValue& rhs);
-
-YG_EXTERN_C_BEGIN
-
-#endif
-
 typedef struct YGConfig* YGConfigRef;
 
 typedef struct YGNode* YGNodeRef;