Use tooltip validation error in DataGrid

src/Avalonia.Controls.DataGrid/Themes/Fluent.xaml

@@ -163,6 +163,10 @@
   <Style Selector="DataGridCell:invalid /template/ Rectangle#InvalidVisualElement">
     <Setter Property="IsVisible" Value="True" />
   </Style>
+  <Style Selector="DataGridCell > TextBox DataValidationErrors">
+    <Setter Property="Template" Value="{DynamicResource TooltipDataValidationContentTemplate}" />
+    <Setter Property="ErrorTemplate" Value="{DynamicResource TooltipDataValidationErrorTemplate}" />
+  </Style>
 
   <Style Selector="DataGridColumnHeader">
     <Setter Property="Foreground" Value="{DynamicResource DataGridColumnHeaderForegroundBrush}" />

src/Avalonia.Themes.Fluent/Controls/DataValidationErrors.xaml

@@ -59,7 +59,7 @@
         <Panel Name="PART_InlineErrorTemplatePanel" Background="Transparent">
           <Panel.Styles>
             <Style Selector="Panel#PART_InlineErrorTemplatePanel">
-              <Setter Property="Margin" Value="8,0,4,0" />
+              <Setter Property="Margin" Value="8,0" />
             </Style>
             <Style Selector="Panel#PART_InlineErrorTemplatePanel ToolTip">
               <Setter Property="BorderBrush" Value="{DynamicResource SystemControlErrorTextForegroundBrush}" />