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.cpp

@@ -10,9 +10,7 @@
 #include "YogaJniException.h"
 #include "common.h"
 
-namespace facebook {
-namespace yoga {
-namespace vanillajni {
+namespace facebook::yoga::vanillajni {
 
 YogaJniException::YogaJniException() {
   jclass cl = getCurrentEnv()->FindClass("java/lang/RuntimeException");
@@ -47,6 +45,5 @@ ScopedLocalRef<jthrowable> YogaJniException::getThrowable() const noexcept {
       getCurrentEnv(),
       static_cast<jthrowable>(getCurrentEnv()->NewLocalRef(throwable_.get())));
 }
-} // namespace vanillajni
-} // namespace yoga
-} // namespace facebook
+
+} // namespace facebook::yoga::vanillajni