[cmdpal] Fix primary button doesn't work issue (#40243)

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## Summary of the Pull Request
ok... it seems didn't work since 0.91.

Maybe we forgot to send message when command has more commands?

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Co-authored-by: Yu Leng <yuleng@microsoft.com>

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/CommandBarViewModel.cs

@@ -155,6 +155,7 @@ public partial class CommandBarViewModel : ObservableObject,
             ContextMenuStack.Add(new ContextMenuStackViewModel(command));
             OnPropertyChanging(nameof(ContextMenu));
             OnPropertyChanged(nameof(ContextMenu));
+            WeakReferenceMessenger.Default.Send<PerformCommandMessage>(new(command.Command.Model, command.Model));
             return ContextKeybindingResult.KeepOpen;
         }
         else