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/TopLevelViewModel.cs

@@ -52,7 +52,18 @@ public sealed partial class TopLevelViewModel : ObservableObject, IListItem
 
     ICommand? ICommandItem.Command => _commandItemViewModel.Command.Model.Unsafe;
 
-    IContextItem?[] ICommandItem.MoreCommands => _commandItemViewModel.MoreCommands.Select(i => i.Model.Unsafe).ToArray();
+    IContextItem?[] ICommandItem.MoreCommands => _commandItemViewModel.MoreCommands
+                                                    .Select(item =>
+                                                    {
+                                                        if (item is ISeparatorContextItem)
+                                                        {
+                                                            return item as IContextItem;
+                                                        }
+                                                        else
+                                                        {
+                                                            return ((CommandContextItemViewModel)item).Model.Unsafe;
+                                                        }
+                                                    }).ToArray();
 
     ////// IListItem
     ITag[] IListItem.Tags => Tags.ToArray();