C++ style enums 8/N: Direction (#1392)

Summary:
X-link: https://github.com/facebook/react-native/pull/39483

Pull Request resolved: https://github.com/facebook/yoga/pull/1392

Moves internal usages of YGDirection to Direction.

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Changelog: [Internal]

Reviewed By: rshest

Differential Revision: D49335231

fbshipit-source-id: 459fe820c91be88734cebaa8655cd3f0afda83bf

tests/YGStyleAccessorsTest.cpp

@@ -82,10 +82,10 @@ namespace facebook::yoga {
 
 ACCESSOR_TEST(
     direction,
-    YGDirectionInherit,
-    YGDirectionLTR,
-    YGDirectionRTL,
-    YGDirectionInherit);
+    Direction::Inherit,
+    Direction::LTR,
+    Direction::RTL,
+    Direction::Inherit);
 
 ACCESSOR_TEST(
     flexDirection,