C++ 17 style nested namespaces (#1326)

Summary:
X-link: https://github.com/facebook/react-native/pull/38304

Pull Request resolved: https://github.com/facebook/yoga/pull/1326

For better readability

Reviewed By: christophpurrer

Differential Revision: D47384926

fbshipit-source-id: 2f60d50a185331b3624d45d1fc45f98d504b3034

java/jni/YogaJniException.h

@@ -9,9 +9,7 @@
 #include <string>
 #include "common.h"
 
-namespace facebook {
-namespace yoga {
-namespace vanillajni {
+namespace facebook::yoga::vanillajni {
 /**
  * This class wraps a Java exception (jthrowable) into a C++ exception; A global
  * reference to Java exception (jthrowable) is made so that the exception object
@@ -33,6 +31,5 @@ public:
 private:
   ScopedGlobalRef<jthrowable> throwable_;
 };
-} // namespace vanillajni
-} // namespace yoga
-} // namespace facebook
+
+} // namespace facebook::yoga::vanillajni