Disable ClipToBounds in TreeDataGridTemplateCell. (#484)

Fixes #483

Author: SKProCH

Material.Avalonia.TreeDataGrid/TreeDataGridTemplateCell.axaml

@@ -1,6 +1,7 @@
 <ResourceDictionary xmlns="https://github.com/avaloniaui"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
   <ControlTheme x:Key="{x:Type TreeDataGridTemplateCell}" TargetType="TreeDataGridTemplateCell">
+    <Setter Property="ClipToBounds" Value="False"></Setter>
     <Setter Property="Template">
       <ControlTemplate>
         <ContentPresenter x:Name="PART_ContentPresenter"