Move background color change into ControlTemplate trigger collection (#3967)

Moving the background changes inside of the ControlTemplate trigger collection changes the binding precedence order such that our "IsMouseOver" trigger is even closer to the DGR_Border than a local value set directly on the DataGrid (i.e. AlternatingRBackground) and thus takes precedence.

Author: nicolaihenriksen

src/MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.DataGrid.xaml

@@ -1,4 +1,4 @@
-<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:converters="clr-namespace:MaterialDesignThemes.Wpf.Converters"
                     xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf">
@@ -431,6 +431,14 @@
                                  Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.Row}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}, FallbackValue=Visible}" />
             </SelectiveScrollingGrid>
           </Border>
+          <ControlTemplate.Triggers>
+            <Trigger Property="IsMouseOver" Value="True">
+              <Setter TargetName="DGR_Border" Property="Background" Value="{DynamicResource MaterialDesign.Brush.DataGrid.RowHoverBackground}" />
+            </Trigger>
+            <Trigger Property="IsSelected" Value="True">
+              <Setter TargetName="DGR_Border" Property="Background" Value="{DynamicResource MaterialDesign.Brush.DataGrid.Selected}" />
+            </Trigger>
+          </ControlTemplate.Triggers>
         </ControlTemplate>
       </Setter.Value>
     </Setter>
@@ -446,12 +454,6 @@
       </Setter.Value>
     </Setter>
     <Style.Triggers>
-      <Trigger Property="IsSelected" Value="True">
-        <Setter Property="Background" Value="{DynamicResource MaterialDesign.Brush.DataGrid.Selected}" />
-      </Trigger>
-      <Trigger Property="IsMouseOver" Value="True">
-        <Setter Property="Background" Value="{DynamicResource MaterialDesign.Brush.DataGrid.RowHoverBackground}" />
-      </Trigger>
       <Trigger Property="IsNewItem" Value="True">
         <Setter Property="Margin" Value="{Binding NewItemMargin, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}, FallbackValue=0}" />
       </Trigger>