CmdPal: Refactoring ContextMenu adding separators, IsCritical styling, and right-click context menus for list items (#40189)

Refactored ContextMenu into it's own control to allow displaying in
CommandBar and in response to right click on list items.

- Adds "critical" styling to context menu items flagged as `IsCritical`.
This will use the theme to style with correct color.
- Added `SeparatorContextItem` and modified `MoreCommands` to allow for
both `CommandContextItem`s and `SeparatorContextItem`s.
- Right clicking a list item with a context menu will open the context
menu at the position of the click and position the filter box at the top
of the context menu.


![image](https://github.com/user-attachments/assets/3bef6b04-28bb-4a17-b731-d9ed20c0566f)


![image](https://github.com/user-attachments/assets/37ed497c-6d98-4f04-8114-d9952127ca2e)


This PR covers:

- closes #38308
- closes #39211
- closes #38307
- closes #38261

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml

@@ -118,22 +118,23 @@
                     ItemClick="ItemsList_ItemClick"
                     ItemTemplate="{StaticResource ListItemViewModelTemplate}"
                     ItemsSource="{x:Bind ViewModel.FilteredItems, Mode=OneWay}"
+                    RightTapped="ItemsList_RightTapped"
                     SelectionChanged="ItemsList_SelectionChanged">
                     <ListView.ItemContainerTransitions>
                         <TransitionCollection />
                     </ListView.ItemContainerTransitions>
                     <!--<ListView.GroupStyle>
-                    <GroupStyle HidesIfEmpty="True">
-                        <GroupStyle.HeaderTemplate>
-                            <DataTemplate>
-                                <TextBlock
-                                    Margin="0,16,0,0"
-                                    Foreground="{ThemeResource TextFillColorSecondaryBrush}"
-                                    Text="{Binding Key, Mode=OneWay}" />
-                            </DataTemplate>
-                        </GroupStyle.HeaderTemplate>
-                    </GroupStyle>
-                </ListView.GroupStyle>-->
+                        <GroupStyle HidesIfEmpty="True">
+                            <GroupStyle.HeaderTemplate>
+                                <DataTemplate>
+                                    <TextBlock
+                                        Margin="0,16,0,0"
+                                        Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                                        Text="{Binding Key, Mode=OneWay}" />
+                                </DataTemplate>
+                            </GroupStyle.HeaderTemplate>
+                        </GroupStyle>
+                    </ListView.GroupStyle>-->
                 </ListView>
             </controls:Case>
             <controls:Case Value="True">

src/modules/cmdpal/Microsoft.CmdPal.UI/ExtViews/ListPage.xaml.cs

@@ -294,4 +294,31 @@ public sealed partial class ListPage : Page,
 
         return null;
     }
+
+    private void ItemsList_RightTapped(object sender, RightTappedRoutedEventArgs e)
+    {
+        if (e.OriginalSource is FrameworkElement element &&
+            element.DataContext is ListItemViewModel item)
+        {
+            if (ItemsList.SelectedItem != item)
+            {
+                ItemsList.SelectedItem = item;
+            }
+
+            ViewModel?.UpdateSelectedItemCommand.Execute(item);
+
+            var pos = e.GetPosition(element);
+
+            _ = DispatcherQueue.TryEnqueue(
+                () =>
+                    {
+                        WeakReferenceMessenger.Default.Send<OpenContextMenuMessage>(
+                            new OpenContextMenuMessage(
+                                element,
+                                Microsoft.UI.Xaml.Controls.Primitives.FlyoutPlacementMode.BottomEdgeAlignedLeft,
+                                pos,
+                                ContextMenuFilterLocation.Top));
+                    });
+        }
+    }
 }