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/YogaExperimentalFeature.java

@@ -15,7 +15,7 @@ import com.facebook.proguard.annotations.DoNotStrip;
 public enum YogaExperimentalFeature {
   WEB_FLEX_BASIS(0);
 
-  private int mIntValue;
+  private final int mIntValue;
 
   YogaExperimentalFeature(int intValue) {
     mIntValue = intValue;