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/Messages/NavigationDepthMessage.cs

@@ -0,0 +1,11 @@
+// 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.
+
+namespace Microsoft.CmdPal.UI.ViewModels.Messages;
+
+/// <summary>
+/// Message containing the current navigation depth (BackStack count) when navigating to a page.
+/// Used to track maximum navigation depth reached during a session for telemetry.
+/// </summary>
+public record NavigationDepthMessage(int Depth);