Reorgnaize C++ tests

Summary:
This does some preprataion for the Yoga CMake Build. The main change is removing the dedicated testutil top-level-directory and static library. This contains a method to count nodes using the event functions exposed to C++, along with a Java binding for the test utility (since the events don't have a Java binding). It is only used in a single place in a way that isn't very useful, so it simplifies things to treat is as source in the existing C++ test library.

This also separates the hand-written and generated UTs, like we are doing in the JS directory in D42207782.

Reviewed By: christophpurrer

Differential Revision: D42247762

fbshipit-source-id: f8a270e99d0315ba7fc608f2471333e7a7be9d79

tests/YGPersistenceTest.cpp

@@ -6,10 +6,11 @@
  */
 
 #include <gtest/gtest.h>
-#include <yoga/testutil/testutil.h>
 #include <yoga/Yoga.h>
 #include <yoga/YGNode.h>
 
+#include "util/TestUtil.h"
+
 using facebook::yoga::test::TestUtil;
 
 TEST(YogaTest, cloning_shared_root) {