Update MarginMultiplierConverter to support Thickness input

src/Avalonia.Controls/Converters/MarginMultiplierConverter.cs

@@ -18,10 +18,24 @@ namespace Avalonia.Controls.Converters
 
         public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
         {
-            if (!(value is int depth))
-                return new Thickness(0);
-
-            return new Thickness(Left ? Indent * depth : 0, Top ? Indent * depth : 0, Right ? Indent * depth : 0, Bottom ? Indent * depth : 0);
+            if (value is int scalarDepth)
+            {
+                return new Thickness(
+                    Left ? Indent * scalarDepth : 0,
+                    Top ? Indent * scalarDepth : 0,
+                    Right ? Indent * scalarDepth : 0,
+                    Bottom ? Indent * scalarDepth : 0);
+            }
+            else if (value is Thickness thinknessDepth)
+            {
+                return new Thickness(
+                    Left ? Indent * thinknessDepth.Left : 0,
+                    Top ? Indent * thinknessDepth.Top : 0,
+                    Right ? Indent * thinknessDepth.Right : 0,
+                    Bottom ? Indent * thinknessDepth.Bottom : 0);
+            }
+            return new Thickness(0);
+            
         }
 
         public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)