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/YGConfigHandle.cs

@@ -0,0 +1,84 @@
+/**
+ * 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 YGConfigHandle : SafeHandle
+    {
+        internal static readonly YGConfigHandle Default = Native.YGConfigGetDefault();
+        private GCHandle _managedConfigHandle;
+
+        private YGConfigHandle() : base(IntPtr.Zero, true)
+        {
+        }
+
+        public override bool IsInvalid
+        {
+            get
+            {
+                return this.handle == IntPtr.Zero;
+            }
+        }
+
+        protected override bool ReleaseHandle()
+        {
+            if (this.handle != Default.handle)
+            {
+                ReleaseManaged();
+                if (!IsInvalid)
+                {
+                    Native.YGConfigFree(this.handle);
+                }
+            }
+            GC.KeepAlive(this);
+            return true;
+        }
+
+        public void SetContext(YogaConfig config)
+        {
+            if (!_managedConfigHandle.IsAllocated)
+            {
+#if UNITY_5_4_OR_NEWER
+                // Weak causes 'GCHandle value belongs to a different domain' error
+                _managedConfigHandle = GCHandle.Alloc(config);
+#else
+                _managedConfigHandle = GCHandle.Alloc(config, GCHandleType.Weak);
+#endif
+                var managedConfigPtr = GCHandle.ToIntPtr(_managedConfigHandle);
+                Native.YGConfigSetContext(this.handle, managedConfigPtr);
+            }
+        }
+
+        private void ReleaseManaged()
+        {
+            if (_managedConfigHandle.IsAllocated)
+            {
+                _managedConfigHandle.Free();
+            }
+        }
+
+        public static YogaConfig GetManaged(IntPtr unmanagedConfigPtr)
+        {
+            if (unmanagedConfigPtr != IntPtr.Zero)
+            {
+                var managedConfigPtr = Native.YGConfigGetContext(unmanagedConfigPtr);
+                var config = GCHandle.FromIntPtr(managedConfigPtr).Target as YogaConfig;
+                if (config == null)
+                {
+                    throw new InvalidOperationException("YogaConfig is already deallocated");
+                }
+                return config;
+            }
+            return null;
+        }
+    }
+}