User/ryanbod/mock settings disk access (#6188)

* 1) Making Directory Methods private.
2) Removing the CreateDirectory / DeleteDirectory functionality from all Settings Unit Tests.

* Abstracting disk access via IIOProvider to be able to provide mocks for unit tests instead of writing to disk.   This also prevents developers who are running unit tests from interfering with the PowerToys settings on their local dev box.

* Dependency Injecting stub SettingsUtils for all tests

* Removing ISettingsUtils from constructors of objects that need to be deserialized (ColorPickerSettings/PowerLauncherSettings) as this breaks System.Text.Json

* Removing unused namespace reference

* Removing redifined mock

* As per PR feedback.  Stub Settings utils should work with any settings type if the intent is to compile / avoid null ref exceptions.

Strangely when implementing this fix it became apparent that a stub settings isn't enough, and disk access needed to be mocked.  I can't explain why the tests were passing previously.

* Leveraging GetMockIOProviderForSaveLoadExists

src/core/Microsoft.PowerToys.Settings.UI.UnitTests/ViewModelTests/PowerLauncherViewModelTest.cs

@@ -5,6 +5,7 @@
 using Microsoft.PowerToys.Settings.UI.Lib;
 using Microsoft.PowerToys.Settings.UI.Lib.ViewModels;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Moq;
 
 namespace ViewModelTests
 {
@@ -24,13 +25,11 @@ namespace ViewModelTests
         private PowerLauncherViewModel viewModel;
         private PowerLauncherSettings mockSettings;
         private SendCallbackMock sendCallbackMock;
-
         [TestInitialize]
         public void Initialize()
         {
             mockSettings = new PowerLauncherSettings();
             sendCallbackMock = new SendCallbackMock();
-
             viewModel = new PowerLauncherViewModel(
                 mockSettings,
                 new PowerLauncherViewModel.SendCallback(sendCallbackMock.OnSend));