Re-enable and modernize PowerDisplay module

Restores PowerDisplay across the PowerToys solution, including build, packaging, signing, and UI integration in Settings, OOBE, and Dashboard. Refactors PowerDisplay app to use CommunityToolkit.Mvvm for ViewModels, moves control logic from code-behind to ViewModels, and modernizes XAML for improved accessibility and theming. Updates group policy support, resource strings, and installer logic. Removes obsolete code and improves maintainability and user experience.