Make BindingExpressionBase the public API.

This matches WPF's API.

src/Avalonia.Base/AvaloniaObject.cs

@@ -416,7 +416,7 @@ namespace Avalonia
         /// <returns>
         /// A disposable which can be used to terminate the binding.
         /// </returns>
-        public IBindingExpression Bind(AvaloniaProperty property, IBinding binding)
+        public BindingExpressionBase Bind(AvaloniaProperty property, IBinding binding)
         {
             if (binding is not IBinding2 b)
                 throw new NotSupportedException($"Unsupported IBinding implementation '{binding}'.");

src/Avalonia.Base/AvaloniaProperty.cs

@@ -566,7 +566,7 @@ namespace Avalonia
         /// </summary>
         /// <param name="o">The object instance.</param>
         /// <param name="source">The binding source.</param>
-        internal abstract IBindingExpression RouteBind(
+        internal abstract BindingExpressionBase RouteBind(
             AvaloniaObject o,
             UntypedBindingExpressionBase source);
 

src/Avalonia.Base/Data/Core/BindingExpressionBase.cs → src/Avalonia.Base/Data/BindingExpressionBase.cs

@@ -1,9 +1,10 @@
-using Avalonia.PropertyStore;
+using System;
+using Avalonia.PropertyStore;
 using Avalonia.Styling;
 
-namespace Avalonia.Data.Core;
+namespace Avalonia.Data;
 
-public abstract class BindingExpressionBase : IBindingExpression, ISetterInstance
+public abstract class BindingExpressionBase : IDisposable, ISetterInstance
 {
     private protected BindingExpressionBase()
     {

src/Avalonia.Base/Data/IBindingExpression.cs

@@ -1,7 +0,0 @@
-using System;
-
-namespace Avalonia.Data;
-
-public interface IBindingExpression : IDisposable
-{
-}

src/Avalonia.Base/DirectPropertyBase.cs

@@ -183,7 +183,7 @@ namespace Avalonia
             return o.Bind(this, source);
         }
 
-        internal override IBindingExpression RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
+        internal override BindingExpressionBase RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
         {
             return o.GetValueStore().AddBinding(this, source);
         }

src/Avalonia.Base/PropertyStore/ValueStore.cs

@@ -43,7 +43,7 @@ namespace Avalonia.PropertyStore
             ReevaluateEffectiveValues();
         }
 
-        public IBindingExpression AddBinding<T>(
+        public BindingExpressionBase AddBinding<T>(
             StyledProperty<T> property,
             UntypedBindingExpressionBase source)
         {
@@ -156,7 +156,7 @@ namespace Avalonia.PropertyStore
             }
         }
 
-        public IBindingExpression AddBinding<T>(DirectPropertyBase<T> property, UntypedBindingExpressionBase source)
+        public BindingExpressionBase AddBinding<T>(DirectPropertyBase<T> property, UntypedBindingExpressionBase source)
         {
             DisposeExistingLocalValueBinding(property);
             _localValueBindings ??= new();

src/Avalonia.Base/StyledProperty.cs

@@ -228,7 +228,7 @@ namespace Avalonia
             return target.Bind<TValue>(this, source, priority);
         }
 
-        internal override IBindingExpression RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
+        internal override BindingExpressionBase RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
         {
             return o.GetValueStore().AddBinding(this, source);
         }

tests/Avalonia.Base.UnitTests/AvaloniaPropertyTests.cs

@@ -175,7 +175,7 @@ namespace Avalonia.Base.UnitTests
                 throw new NotImplementedException();
             }
 
-            internal override IBindingExpression RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
+            internal override BindingExpressionBase RouteBind(AvaloniaObject o, UntypedBindingExpressionBase source)
             {
                 throw new NotImplementedException();
             }