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/Converters/ContextItemTemplateSelector.cs

@@ -2,9 +2,12 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using Microsoft.Bot.AdaptiveExpressions.Core;
 using Microsoft.CmdPal.UI.ViewModels;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Controls.Primitives;
+using Microsoft.UI.Xaml.Data;
 
 namespace Microsoft.CmdPal.UI;
 
@@ -14,8 +17,29 @@ internal sealed partial class ContextItemTemplateSelector : DataTemplateSelector
 
     public DataTemplate? Critical { get; set; }
 
-    protected override DataTemplate? SelectTemplateCore(object item)
+    public DataTemplate? Separator { get; set; }
+
+    protected override DataTemplate? SelectTemplateCore(object item, DependencyObject dependencyObject)
     {
-        return ((CommandContextItemViewModel)item).IsCritical ? Critical : Default;
+        DataTemplate? dataTemplate = Default;
+
+        if (dependencyObject is ListViewItem li)
+        {
+            li.IsEnabled = true;
+
+            if (item is SeparatorContextItemViewModel)
+            {
+                li.IsEnabled = false;
+                li.AllowFocusWhenDisabled = false;
+                li.AllowFocusOnInteraction = false;
+                dataTemplate = Separator;
+            }
+            else
+            {
+                dataTemplate = ((CommandContextItemViewModel)item).IsCritical ? Critical : Default;
+            }
+        }
+
+        return dataTemplate;
     }
 }