Share TypedBindingExpression.Attach validation across instantiations.

Factor the validation logic (most notably the exception string
formatting) out of the generic Attach method into a non-generic static
helper. It only uses typeof(TValue), not TValue, so sharing it avoids
duplicating the code per generic instantiation, a meaningful NativeAOT
size saving (~3.3 KB => ~2.5 KB per instantiation).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Avalonia.Base/Data/Core/TypedBindingExpression.cs

@@ -62,25 +62,40 @@ internal class TypedBindingExpression<TSource, TValue> : BindingExpressionBase,
         AvaloniaProperty targetProperty,
         BindingPriority priority)
     {
-        if (_sink is not null)
+        // The validation is factored out into a non-generic static method so that its code (most
+        // notably the exception string formatting) is shared across all generic instantiations
+        // instead of being duplicated for each one, which is a meaningful NativeAOT size saving.
+        var element = ValidateAttach(_sink is not null, TargetProperty, typeof(TValue), target, targetProperty);
+
+        _sink = sink;
+        _frame = frame;
+        _target = new(element);
+        TargetProperty = targetProperty;
+        Priority = priority;
+    }
+
+    private static StyledElement ValidateAttach(
+        bool alreadyAttached,
+        AvaloniaProperty? currentTargetProperty,
+        Type valueType,
+        AvaloniaObject target,
+        AvaloniaProperty targetProperty)
+    {
+        if (alreadyAttached)
             throw new InvalidOperationException("TypedBindingExpression was already attached.");
         if (target is not StyledElement element)
             throw new InvalidOperationException("TypedBindingExpression may only target StyledElements");
-        if (TargetProperty is not null && TargetProperty != targetProperty)
+        if (currentTargetProperty is not null && currentTargetProperty != targetProperty)
             throw new InvalidOperationException("TypedBindingExpression was already attached to a different property.");
 
-        if (!typeof(TValue).IsAssignableTo(targetProperty.PropertyType))
+        if (!valueType.IsAssignableTo(targetProperty.PropertyType))
         {
             throw new InvalidOperationException(
-                $"TypedBindingExpression of type '{typeof(TValue)}' cannot be bound " +
+                $"TypedBindingExpression of type '{valueType}' cannot be bound " +
                 $"to a property of type '{targetProperty.PropertyType}'.");
         }
 
-        _sink = sink;
-        _frame = frame;
-        _target = new(element);
-        TargetProperty = targetProperty;
-        Priority = priority;
+        return element;
     }
 
     public override void Dispose()