BREAKING - Change measure() api to remove need for MeasureOutput allocation

Summary: This is an API breaking change done to allow us to avoid an allocation during measurement. Instead we do the same trick as is done when passing measure results to C, we path them into a long.

Reviewed By: splhack

Differential Revision: D4081037

fbshipit-source-id: 28adbcdd160cbd3f59a0fdd4b9f1200ae18678f1

csharp/Facebook.CSSLayout/MeasureFunction.cs

@@ -9,5 +9,10 @@
 
 namespace Facebook.CSSLayout
 {
-    public delegate void MeasureFunction(CSSNode node, float width, CSSMeasureMode widthMode, float height, CSSMeasureMode heightMode, MeasureOutput measureOutput);
+  public delegate long MeasureFunction(
+      CSSNode node,
+      float width,
+      CSSMeasureMode widthMode,
+      float height,
+      CSSMeasureMode heightMode);
 }