Remove ISettingsUtils and ISettingsPath interfaces (#44331)

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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

This PR removes the ISettingsUtils and ISettingsPath interfaces to
reduce some complexity. They only existed so the classes can be used
with moq. But this is also possible by using virtual methods which is
cleaner.

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## PR Checklist

- [ ] Closes: #xxx
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- [ ] **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)
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- [ ] [YML for signed
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- [ ] **Documentation updated:** If checked, please file a pull request
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and link it here: #xxx

src/settings-ui/Settings.UI.Library/SettingPath.cs

@@ -9,7 +9,7 @@ using Microsoft.PowerToys.Settings.UI.Library.Utilities;
 
 namespace Microsoft.PowerToys.Settings.UI.Library
 {
-    public class SettingPath : ISettingsPath
+    public class SettingPath
     {
         private const string DefaultFileName = "settings.json";
 
@@ -23,6 +23,11 @@ namespace Microsoft.PowerToys.Settings.UI.Library
             _path = path ?? throw new ArgumentNullException(nameof(path));
         }
 
+        public SettingPath()
+            : this(new FileSystem().Directory, new FileSystem().Path)
+        {
+        }
+
         public bool SettingsFolderExists(string powertoy)
         {
             return _directory.Exists(System.IO.Path.Combine(Helper.LocalApplicationDataFolder(), $"Microsoft\\PowerToys\\{powertoy}"));