[CmdPal][UnitTests] Add/Migrate unit test for Apps and Bookmarks extension (#41238)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
1. Create Apps and Bookmarks ut project.
2. Refactor Apps and Bookmarks. And some interface in these extensions
to add a abstraction layer for testing purpose.
New interface list:
* ISettingsInterface
* IUWPApplication
* IAppCache
* IBookmarkDataSource
3. Add/Migrate some test case for Apps and Bookmarks extension

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## PR Checklist

- [x] Closes: #41239 #41240
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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---------

Co-authored-by: Yu Leng <yuleng@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Apps/IAppCache.cs

@@ -0,0 +1,37 @@
+// 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 System.Threading.Tasks;
+using Microsoft.CmdPal.Ext.Apps.Programs;
+
+namespace Microsoft.CmdPal.Ext.Apps;
+
+/// <summary>
+/// Interface for application cache that provides access to Win32 and UWP applications.
+/// </summary>
+public interface IAppCache : IDisposable
+{
+    /// <summary>
+    /// Gets the collection of Win32 programs.
+    /// </summary>
+    IList<Win32Program> Win32s { get; }
+
+    /// <summary>
+    /// Gets the collection of UWP applications.
+    /// </summary>
+    IList<IUWPApplication> UWPs { get; }
+
+    /// <summary>
+    /// Determines whether the cache should be reloaded.
+    /// </summary>
+    /// <returns>True if cache should be reloaded, false otherwise.</returns>
+    bool ShouldReload();
+
+    /// <summary>
+    /// Resets the reload flag.
+    /// </summary>
+    void ResetReloadFlag();
+}