Reduce memory pressure when using bindings.

src/Avalonia.Base/Data/BindingOperations.cs

@@ -45,7 +45,7 @@ namespace Avalonia.Data
                 case BindingMode.OneWay:
                     return target.Bind(property, binding.Observable ?? binding.Subject, binding.Priority);
                 case BindingMode.TwoWay:
-                    return new CompositeDisposable(
+                    return new TwoWayBindingDisposable(
                         target.Bind(property, binding.Subject, binding.Priority),
                         target.GetObservable(property).Subscribe(binding.Subject));
                 case BindingMode.OneTime:
@@ -88,6 +88,32 @@ namespace Avalonia.Data
                     throw new ArgumentException("Invalid binding mode.");
             }
         }
+
+        private sealed class TwoWayBindingDisposable : IDisposable
+        {
+            private readonly IDisposable _first;
+            private readonly IDisposable _second;
+            private bool _isDisposed;
+
+            public TwoWayBindingDisposable(IDisposable first, IDisposable second)
+            {
+                _first = first;
+                _second = second;
+            }
+
+            public void Dispose()
+            {
+                if (_isDisposed)
+                {
+                    return;
+                }
+
+                _first.Dispose();
+                _second.Dispose();
+
+                _isDisposed = true;
+            }
+        }
     }
 
     public sealed class DoNothingType

src/Avalonia.Base/Reactive/AvaloniaPropertyObservable.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 
 namespace Avalonia.Reactive
 {
@@ -55,9 +56,9 @@ namespace Avalonia.Reactive
                     newValue = (T)e.Sender.GetValue(e.Property);
                 }
 
-                if (!Equals(newValue, _value))
+                if (!EqualityComparer<T>.Default.Equals(newValue, _value))
                 {
-                    _value = (T)newValue;
+                    _value = newValue;
                     PublishNext(_value);
                 }
             }