Add VRChat and GitHub packages to Unity project

Assets/Udon/Serialization/OdinSerializer/Utilities/Misc/ReferenceEqualityComparer.cs

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+//-----------------------------------------------------------------------
+// <copyright file="ReferenceEqualityComparer.cs" company="Sirenix IVS">
+// Copyright (c) 2018 Sirenix IVS
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+//-----------------------------------------------------------------------
+
+namespace VRC.Udon.Serialization.OdinSerializer.Utilities
+{
+    using System;
+    using System.Collections.Generic;
+
+    /// <summary>
+    /// Compares objects by reference only, ignoring equality operators completely. This is used by the property tree reference dictionaries to keep track of references.
+    /// </summary>
+    public class ReferenceEqualityComparer<T> : IEqualityComparer<T> where T : class
+    {
+        /// <summary>
+        /// A default, cached instance of this generic variant of the reference equality comparer.
+        /// </summary>
+        public static readonly ReferenceEqualityComparer<T> Default = new ReferenceEqualityComparer<T>();
+
+        /// <summary>
+        /// Returns true if the object references are equal.
+        /// </summary>
+        public bool Equals(T x, T y)
+        {
+            return object.ReferenceEquals(x, y);
+        }
+
+        /// <summary>
+        /// Returns the result of the object's own GetHashCode method.
+        /// </summary>
+        public int GetHashCode(T obj)
+        {
+            try
+            {
+                return obj.GetHashCode();
+            }
+            catch (NullReferenceException)
+            {
+                return -1;
+            }
+        }
+    }
+}