Rename the [Ee]xts dir to ext (#38852)

**WARNING:** This PR will probably blow up all in-flight PRs

at some point in the early days of CmdPal, two of us created seperate
`Exts` and `exts` dirs. Depending on what the casing was on the branch
that you checked one of those out from, it'd get stuck like that on your
PC forever.

Windows didn't care, so we never noticed.

But GitHub does care, and now browsing the source on GitHub is basically
impossible.

Closes #38081

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WinGet/WindowsPackageManager.Interop/ClassModel.cs

@@ -0,0 +1,47 @@
+// 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 System;
+using System.Collections.Generic;
+using WindowsPackageManager.Interop;
+
+namespace Microsoft.CmdPal.Ext.WinGet.WindowsPackageManager.Interop;
+
+#nullable disable
+internal sealed class ClassModel
+{
+    /// <summary>
+    /// Gets the interface for the projected class type generated by CsWinRT
+    /// </summary>
+    public Type InterfaceType { get; init; }
+
+    /// <summary>
+    /// Gets the projected class type generated by CsWinRT
+    /// </summary>
+    public Type ProjectedClassType { get; init; }
+
+    /// <summary>
+    /// Gets the Clsids for each context (e.g. OutOfProcProd, OutOfProcDev)
+    /// </summary>
+    public IReadOnlyDictionary<ClsidContext, Guid> Clsids { get; init; }
+
+    /// <summary>
+    /// Get CLSID based on the provided context
+    /// </summary>
+    /// <param name="context">Context</param>
+    /// <returns>CLSID for the provided context.</returns>
+    /// <exception cref="InvalidOperationException">Throw an exception if the clsid context is not available for the current instance.</exception>
+    public Guid GetClsid(ClsidContext context)
+    {
+        return !Clsids.TryGetValue(context, out var clsid)
+            ? throw new InvalidOperationException($"{ProjectedClassType.FullName} is not implemented in context {context}")
+            : clsid;
+    }
+
+    /// <summary>
+    /// Get IID corresponding to the COM object
+    /// </summary>
+    /// <returns>IID.</returns>
+    public Guid GetIid() => InterfaceType.GUID;
+}