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/ext/SamplePagesExtension/Pages/SampleListPage.cs

@@ -81,6 +81,7 @@ internal sealed partial class SampleListPage : ListPage
                         Title = "I'm a second command",
                         RequestedShortcut = KeyChordHelpers.FromModifiers(ctrl: true, vkey: VirtualKey.Number1),
                     },
+                    new SeparatorContextItem(),
                     new CommandContextItem(
                         new ToastCommand("Third command invoked", MessageState.Error) { Name = "Do 3", Icon = new IconInfo("\uF148") }) // dial 3
                     {