Summary: @public Passing primitive data via JNI is more efficient than passing objects. Here, we avoid creating `YogaValue` (Java) instances via JNI, and rather pass a `long` back to Java. The instance is then created by extracting the necessary bytes on the Java side. Reviewed By: foghina Differential Revision: D14576755 fbshipit-source-id: 22d09ad50c3ac6c49b0a797a0dad639ea4829df9