C++ style enums 7/N: MeasureMode (#1389)

Summary:
X-link: https://github.com/facebook/react-native/pull/39452

Pull Request resolved: https://github.com/facebook/yoga/pull/1389

This converts usages of YGMeasureMode to MeasureMode

Reviewed By: rozele

Differential Revision: D49271165

fbshipit-source-id: 273c9ed0a61c3965e469548d29d37e4566c974dc

tests/YGNodeCallbackTest.cpp

@@ -38,7 +38,7 @@ TEST(Node, measure_with_measure_fn) {
       });
 
   ASSERT_EQ(
-      n.measure(23, YGMeasureModeExactly, 24, YGMeasureModeAtMost),
+      n.measure(23, MeasureMode::Exactly, 24, MeasureMode::AtMost),
       (YGSize{23, 12}));
 }