Mark model fields final

Summary: These are already considered immutable, but not marked in their class.

Reviewed By: emilsjolander

Differential Revision: D6759564

fbshipit-source-id: 810dc8a9730fb330760d2aedecafcea81cf25cb1

java/com/facebook/yoga/YogaEdge.java

@@ -23,7 +23,7 @@ public enum YogaEdge {
   VERTICAL(7),
   ALL(8);
 
-  private int mIntValue;
+  private final int mIntValue;
 
   YogaEdge(int intValue) {
     mIntValue = intValue;