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.ViewModels/Messages/CloseContextMenuMessage.cs

@@ -0,0 +1,12 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Microsoft.CmdPal.UI.ViewModels.Messages;
+
+/// <summary>
+/// Used to announce that a context menu should close
+/// </summary>
+public record CloseContextMenuMessage
+{
+}

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Messages/OpenContextMenuMessage.cs

@@ -2,11 +2,21 @@
 // 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.UI.Xaml;
+using Microsoft.UI.Xaml.Controls.Primitives;
+using Windows.Foundation;
+
 namespace Microsoft.CmdPal.UI.ViewModels.Messages;
 
 /// <summary>
-/// Used to perform a list item's secondary command when the user presses ctrl+enter in the search box
+/// Used to announce the context menu should open
 /// </summary>
-public record OpenContextMenuMessage
+public record OpenContextMenuMessage(FrameworkElement? Element, FlyoutPlacementMode? FlyoutPlacementMode, Point? Point, ContextMenuFilterLocation ContextMenuFilterLocation)
 {
 }
+
+public enum ContextMenuFilterLocation
+{
+    Top,
+    Bottom,
+}

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Messages/UpdateCommandBarMessage.cs

@@ -16,11 +16,11 @@ public record UpdateCommandBarMessage(ICommandBarContext? ViewModel)
 
 public interface IContextMenuContext : INotifyPropertyChanged
 {
-    public IEnumerable<CommandContextItemViewModel> MoreCommands { get; }
+    public IEnumerable<IContextItemViewModel> MoreCommands { get; }
 
     public bool HasMoreCommands { get; }
 
-    public List<CommandContextItemViewModel> AllCommands { get; }
+    public List<IContextItemViewModel> AllCommands { get; }
 
     /// <summary>
     /// Generates a mapping of key -> command item for this particular item's
@@ -33,6 +33,7 @@ public interface IContextMenuContext : INotifyPropertyChanged
     public Dictionary<KeyChord, CommandContextItemViewModel> Keybindings()
     {
         return MoreCommands
+            .OfType<CommandContextItemViewModel>()
             .Where(c => c.HasRequestedShortcut)
             .ToDictionary(
             c => c.RequestedShortcut ?? new KeyChord(0, 0, 0),