[fxcop] Settings UI library (part 4) - project/namespace renames

[lmawarid]

Summary of the Pull Request

The final part of the effort to enable FxCop on the Settings project, involves renaming namespaces and projects to address CA1716.

PR Checklist

• Applies to [Chore] Enable Static analysis (FxCopAnalyzers) on C# Projects #5129
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
  
• Requires documentation to be updated - see Update docs to reflect Settings.UI.Library project name change #7458
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Info on Pull Request

• Rename Microsoft.PowerToys.Settings.UI.Lib project to Microsoft.PowerToys.Settings.UI.Library (including associated namespaces and directories)
• Rename Microsoft.PowerToys.Settings.UI.Interface to Microsoft.PowerToys.Settings.UI.Interfaces (namespace and directory)
• Add FxCop to project file

Also includes some minor fixes that I might have missed out from the last PR.

Validation Steps Performed

Ensure the Library unit tests pass on Debug & Release mode, and manually validate settings functionality for Debug & Release builds.

[ryanbodrug-microsoft]

LGTM