CmdPal: Move the OpenContextMenuMessage into the UI project (#40791)

I just blindly moved all the messages. But _this_ one really makes more
sense as a UI message. It's got framework elements. It us used to
actually open a UI element. The whole thing is very UI specific.

re: #40113

src/modules/cmdpal/Microsoft.CmdPal.Core.ViewModels/ContextMenuViewModel.cs

@@ -14,8 +14,7 @@ using Windows.System;
 namespace Microsoft.CmdPal.Core.ViewModels;
 
 public partial class ContextMenuViewModel : ObservableObject,
-    IRecipient<UpdateCommandBarMessage>,
-    IRecipient<OpenContextMenuMessage>
+    IRecipient<UpdateCommandBarMessage>
 {
     public ICommandBarContext? SelectedItem
     {
@@ -43,7 +42,6 @@ public partial class ContextMenuViewModel : ObservableObject,
     public ContextMenuViewModel()
     {
         WeakReferenceMessenger.Default.Register<UpdateCommandBarMessage>(this);
-        WeakReferenceMessenger.Default.Register<OpenContextMenuMessage>(this);
     }
 
     public void Receive(UpdateCommandBarMessage message)
@@ -51,16 +49,6 @@ public partial class ContextMenuViewModel : ObservableObject,
         SelectedItem = message.ViewModel;
     }
 
-    public void Receive(OpenContextMenuMessage message)
-    {
-        FilterOnTop = message.ContextMenuFilterLocation == ContextMenuFilterLocation.Top;
-
-        ResetContextMenu();
-
-        OnPropertyChanging(nameof(FilterOnTop));
-        OnPropertyChanged(nameof(FilterOnTop));
-    }
-
     public void UpdateContextItems()
     {
         if (SelectedItem != null)
@@ -192,7 +180,7 @@ public partial class ContextMenuViewModel : ObservableObject,
         ListHelpers.InPlaceUpdateList(FilteredItems, [.. CurrentContextMenu!]);
     }
 
-    private void ResetContextMenu()
+    public void ResetContextMenu()
     {
         while (ContextMenuStack.Count > 1)
         {