CmdPal: Removing Core projects (#45693)

Functionally, no differences.

- Removed Core projects.
- Core.Common => Microsoft.CmdPal.Common
- Core.ViewModels => Microsoft.CmdPal.UI.ViewModels

---------

Co-authored-by: Jiří Polášek <me@jiripolasek.com>

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

@@ -0,0 +1,13 @@
+// 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.
+
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace Microsoft.CmdPal.UI.ViewModels;
+
+public partial class ToastViewModel : ObservableObject
+{
+    [ObservableProperty]
+    public partial string ToastMessage { get; set; } = string.Empty;
+}