DataGrid inertial scroll support (#13502) (#13511)

src/Avalonia.Controls.DataGrid/DataGrid.cs

@@ -412,6 +412,21 @@ namespace Avalonia.Controls
             }
         }
 
+        /// <summary>
+        /// Defines the <see cref="IsScrollInertiaEnabled"/> property.
+        /// </summary>
+        public static readonly AttachedProperty<bool> IsScrollInertiaEnabledProperty =
+            ScrollViewer.IsScrollInertiaEnabledProperty.AddOwner<DataGrid>();
+
+        /// <summary>
+        /// Gets or sets whether scroll gestures should include inertia in their behavior and value.
+        /// </summary>
+        public bool IsScrollInertiaEnabled
+        {
+            get => GetValue(IsScrollInertiaEnabledProperty);
+            set => SetValue(IsScrollInertiaEnabledProperty, value);
+        }
+
         private bool _isValid = true;
 
         public static readonly DirectProperty<DataGrid, bool> IsValidProperty =

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

@@ -532,9 +532,13 @@
               <DataGridRowsPresenter Name="PART_RowsPresenter"
                                      Grid.Row="1"
                                      Grid.RowSpan="2"
-                                     Grid.ColumnSpan="3" Grid.Column="0">
+                                     Grid.ColumnSpan="3"
+                                     Grid.Column="0"
+                                     ScrollViewer.IsScrollInertiaEnabled="{TemplateBinding IsScrollInertiaEnabled}">
                 <DataGridRowsPresenter.GestureRecognizers>
-                  <ScrollGestureRecognizer CanHorizontallyScroll="True" CanVerticallyScroll="True" />
+                  <ScrollGestureRecognizer CanHorizontallyScroll="True"
+                                           CanVerticallyScroll="True"
+                                           IsScrollInertiaEnabled="{Binding (ScrollViewer.IsScrollInertiaEnabled), ElementName=PART_RowsPresenter}" />
                 </DataGridRowsPresenter.GestureRecognizers>
               </DataGridRowsPresenter>
               <Rectangle Name="PART_BottomRightCorner"

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

@@ -335,10 +335,12 @@
 
               <DataGridRowsPresenter Name="PART_RowsPresenter"
                                      Grid.Row="1"
-                                     Grid.ColumnSpan="2">
+                                     Grid.ColumnSpan="2"
+                                     ScrollViewer.IsScrollInertiaEnabled="{TemplateBinding IsScrollInertiaEnabled}">
                 <DataGridRowsPresenter.GestureRecognizers>
                   <ScrollGestureRecognizer CanHorizontallyScroll="True"
-                                           CanVerticallyScroll="True" />
+                                           CanVerticallyScroll="True"
+                                           IsScrollInertiaEnabled="{Binding (ScrollViewer.IsScrollInertiaEnabled), ElementName=PART_RowsPresenter}" />
                 </DataGridRowsPresenter.GestureRecognizers>
               </DataGridRowsPresenter>
               <Rectangle Name="PART_BottomRightCorner"