Implement standard interface for toggling experimental features

Summary: We want to start experimenting with changes to the library in a more controlled and easier to measure manner. This diff adds the basics of an experiment layer to csslayout.

Reviewed By: gkassabli

Differential Revision: D4174260

fbshipit-source-id: ad3667183810c02833fba9a1276f89286e848fcd

csharp/Facebook.CSSLayout/CSSNode.cs

@@ -550,5 +550,17 @@ namespace Facebook.CSSLayout
         {
             return Native.CSSNodeGetInstanceCount();
         }
+
+        public static void setExperimentalFeatureEnabled(
+            CSSExperimentalFeature feature,
+            bool enabled)
+        {
+            return Native.CSSLayoutSetExperimentalFeatureEnabled(feature, enabled);
+        }
+
+        public static bool isExperimentalFeatureEnabled(CSSExperimentalFeature feature)
+        {
+            return Native.CSSLayoutIsExperimentalFeatureEnabled(feature);
+        }
     }
 }