Move YGLogger into YGConfig and associate YGNodeRef with log events

Summary:
Moves the `YGLogger` into `YGConfig` and pass the `YGNodeRef` into the logger to be able to associate the log messages and assertions with the specific node.

Tackles facebook/yoga#530 and facebook/yoga#446
Closes https://github.com/facebook/yoga/pull/531

Reviewed By: astreet

Differential Revision: D4970149

Pulled By: emilsjolander

fbshipit-source-id: b7fcdaa273143ea2fa35861620b2e4d79f04f0af

csharp/Facebook.Yoga/Logger.cs

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+namespace Facebook.Yoga
+{
+    public delegate void Logger(
+        YogaConfig config,
+        YogaNode node,
+        YogaLogLevel level,
+        string message);
+}