C# use YogaSize throughout the measure call chain

Summary:
Java still has the same problem (see #296)

Also there is no need to have double in the method signature as we only use float internally, which could confuse some.
Closes https://github.com/facebook/yoga/pull/300

Reviewed By: splhack

Differential Revision: D4365993

Pulled By: emilsjolander

fbshipit-source-id: 681f8b1725e63eddcfb9a6c756f2ae215a44425a

csharp/tests/Facebook.Yoga/YogaNodeTest.cs

@@ -169,8 +169,8 @@ namespace Facebook.Yoga
                 return MeasureOutput.Make(123.4f, 81.7f);
             });
             node.CalculateLayout();
-            Assert.AreEqual(123, node.LayoutWidth);
-            Assert.AreEqual(81, node.LayoutHeight);
+            Assert.AreEqual(123.4f, node.LayoutWidth);
+            Assert.AreEqual(81.7f, node.LayoutHeight);
         }
 
         [Test]