Use correct newValue on inherited property change.

- `oldValue` was misnamed - it's the new value
- We calculated the new value and then didn't pass it to children for their property changed events: they were using the default value which may be wrong if the value is set further up the tree

src/Avalonia.Base/PropertyStore/EffectiveValue`1.cs

@@ -140,24 +140,24 @@ namespace Avalonia.PropertyStore
 
             var p = (StyledProperty<T>)property;
             BindingPriority priority;
-            T oldValue;
+            T newValue;
 
             if (property.Inherits && owner.TryGetInheritedValue(property, out var i))
             {
-                oldValue = ((EffectiveValue<T>)i).Value;
+                newValue = ((EffectiveValue<T>)i).Value;
                 priority = BindingPriority.Inherited;
             }
             else
             {
-                oldValue = _metadata.DefaultValue;
+                newValue = _metadata.DefaultValue;
                 priority = BindingPriority.Unset;
             }
 
-            if (!EqualityComparer<T>.Default.Equals(oldValue, Value))
+            if (!EqualityComparer<T>.Default.Equals(newValue, Value))
             {
-                owner.Owner.RaisePropertyChanged(p, Value, oldValue, priority, true);
+                owner.Owner.RaisePropertyChanged(p, Value, newValue, priority, true);
                 if (property.Inherits)
-                    owner.OnInheritedEffectiveValueDisposed(p, Value);
+                    owner.OnInheritedEffectiveValueDisposed(p, Value, newValue);
             }
 
             if (ValueEntry?.GetDataValidationState(out _, out _) ??

src/Avalonia.Base/PropertyStore/ValueStore.cs

@@ -419,7 +419,9 @@ namespace Avalonia.PropertyStore
                 ReevaluateEffectiveValue(property, current);
             }
             else
+            {
                 ReevaluateEffectiveValues();
+            }
         }
 
         /// <summary>
@@ -481,7 +483,8 @@ namespace Avalonia.PropertyStore
         /// </summary>
         /// <param name="property">The property whose value changed.</param>
         /// <param name="oldValue">The old value of the property.</param>
-        public void OnInheritedEffectiveValueDisposed<T>(StyledProperty<T> property, T oldValue)
+        /// <param name="newValue">The new value of the property.</param>
+        public void OnInheritedEffectiveValueDisposed<T>(StyledProperty<T> property, T oldValue, T newValue)
         {
             Debug.Assert(property.Inherits);
 
@@ -489,12 +492,11 @@ namespace Avalonia.PropertyStore
 
             if (children is not null)
             {
-                var defaultValue = property.GetDefaultValue(Owner.GetType());
                 var count = children.Count;
 
                 for (var i = 0; i < count; ++i)
                 {
-                    children[i].GetValueStore().OnAncestorInheritedValueChanged(property, oldValue, defaultValue);
+                    children[i].GetValueStore().OnAncestorInheritedValueChanged(property, oldValue, newValue);
                 }
             }
         }