Remove DeferredSetter.

It's not needed any more.

src/Avalonia.Base/Utilities/DeferredSetter.cs

@@ -1,128 +0,0 @@
-// Copyright (c) The Avalonia Project. All rights reserved.
-// Licensed under the MIT license. See licence.md file in the project root for full license information.
-
-using System;
-
-namespace Avalonia.Utilities
-{
-    /// <summary>
-    /// A utility class to enable deferring assignment until after property-changed notifications are sent.
-    /// Used to fix #855.
-    /// </summary>
-    /// <typeparam name="TSetRecord">The type of value with which to track the delayed assignment.</typeparam>
-    internal sealed class DeferredSetter<TSetRecord>
-    {
-        private readonly SingleOrQueue<TSetRecord> _pendingValues;
-        private bool _isNotifying;
-
-        public DeferredSetter()
-        {
-            _pendingValues = new SingleOrQueue<TSetRecord>();
-        }
-
-        private static void SetAndRaisePropertyChanged(AvaloniaObject source, AvaloniaProperty<TSetRecord> property, ref TSetRecord backing, TSetRecord value)
-        {
-            var old = backing;
-
-            backing = value;
-
-            source.RaisePropertyChanged(property, old, value);
-        }
-
-        public bool SetAndNotify(
-            AvaloniaObject source,
-            AvaloniaProperty<TSetRecord> property,
-            ref TSetRecord backing,
-            TSetRecord value)
-        {
-            if (!_isNotifying)
-            {
-                using (new NotifyDisposable(this))
-                {
-                    SetAndRaisePropertyChanged(source, property, ref backing, value);
-                }
-
-                if (!_pendingValues.Empty)
-                {
-                    using (new NotifyDisposable(this))
-                    {
-                        while (!_pendingValues.Empty)
-                        {
-                            SetAndRaisePropertyChanged(source, property, ref backing, _pendingValues.Dequeue());
-                        }
-                    }
-                }
-
-                return true;
-            }
-
-            _pendingValues.Enqueue(value);
-
-            return false;
-        }
-
-        public bool SetAndNotifyCallback<TValue>(AvaloniaProperty property, ISetAndNotifyHandler<TValue> setAndNotifyHandler, ref TValue backing, TValue value)
-            where TValue : TSetRecord
-        {
-            if (!_isNotifying)
-            {
-                using (new NotifyDisposable(this))
-                {
-                    setAndNotifyHandler.HandleSetAndNotify(property, ref backing, value);
-                }
-
-                if (!_pendingValues.Empty)
-                {
-                    using (new NotifyDisposable(this))
-                    {
-                        while (!_pendingValues.Empty)
-                        {
-                            setAndNotifyHandler.HandleSetAndNotify(property, ref backing, (TValue)_pendingValues.Dequeue());
-                        }
-                    }
-                }
-
-                return true;
-            }
-
-            _pendingValues.Enqueue(value);
-
-            return false;
-        }
-
-        /// <summary>
-        /// Disposable that marks the property as currently notifying.
-        /// When disposed, marks the property as done notifying.
-        /// </summary>
-        private readonly struct NotifyDisposable : IDisposable
-        {
-            private readonly DeferredSetter<TSetRecord> _setter;
-
-            internal NotifyDisposable(DeferredSetter<TSetRecord> setter)
-            {
-                _setter = setter;
-                _setter._isNotifying = true;
-            }
-
-            public void Dispose()
-            {
-                _setter._isNotifying = false;
-            }
-        }
-    }
-
-    /// <summary>
-    /// Handler for set and notify requests.
-    /// </summary>
-    /// <typeparam name="TValue">Value type.</typeparam>
-    internal interface ISetAndNotifyHandler<TValue>
-    {
-        /// <summary>
-        /// Handles deferred setter requests to set a value.
-        /// </summary>
-        /// <param name="property">Property being set.</param>
-        /// <param name="backing">Backing field reference.</param>
-        /// <param name="value">New value.</param>
-        void HandleSetAndNotify(AvaloniaProperty property, ref TValue backing, TValue value);
-    }
-}