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/YGNodeHandle.cs

@@ -0,0 +1,80 @@
+/**
+ * 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.
+ */
+
+using System;
+using System.Runtime.InteropServices;
+
+namespace Facebook.Yoga
+{
+    internal class YGNodeHandle : SafeHandle
+    {
+        private GCHandle _managedNodeHandle;
+
+        private YGNodeHandle() : base(IntPtr.Zero, true)
+        {
+        }
+
+        public override bool IsInvalid
+        {
+            get
+            {
+                return this.handle == IntPtr.Zero;
+            }
+        }
+
+        protected override bool ReleaseHandle()
+        {
+            ReleaseManaged();
+            if (!IsInvalid)
+            {
+                Native.YGNodeFree(this.handle);
+                GC.KeepAlive(this);
+            }
+            return true;
+        }
+
+        public void SetContext(YogaNode node)
+        {
+            if (!_managedNodeHandle.IsAllocated)
+            {
+#if UNITY_5_4_OR_NEWER
+                // Weak causes 'GCHandle value belongs to a different domain' error
+                _managedNodeHandle = GCHandle.Alloc(node);
+#else
+                _managedNodeHandle = GCHandle.Alloc(node, GCHandleType.Weak);
+#endif
+                var managedNodePtr = GCHandle.ToIntPtr(_managedNodeHandle);
+                Native.YGNodeSetContext(this.handle, managedNodePtr);
+            }
+        }
+
+        public void ReleaseManaged()
+        {
+            if (_managedNodeHandle.IsAllocated)
+            {
+                _managedNodeHandle.Free();
+            }
+        }
+
+        public static YogaNode GetManaged(IntPtr unmanagedNodePtr)
+        {
+            if (unmanagedNodePtr != IntPtr.Zero)
+            {
+                var managedNodePtr = Native.YGNodeGetContext(unmanagedNodePtr);
+                var node = GCHandle.FromIntPtr(managedNodePtr).Target as YogaNode;
+                if (node == null)
+                {
+                    throw new InvalidOperationException("YogaNode is already deallocated");
+                }
+                return node;
+            }
+            return null;
+        }
+    }
+}