Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Building out the shared SwiftUI demo app for easier future validation of cross-platform tokens and components.

• Created a Demo enum to enumerate our demos.
• Created mostly-empty Button and Shimmer demo views.
• Added a NavigationSplitView to the main ContentView to switch between these.

Verification

Ran the app across iOS and macOS, in both light and dark modes.

Visual Verification

Light	Dark

Pull request checklist

This PR has considered:

• Light and Dark appearances
• iOS supported versions (all major versions greater than or equal current target deployment version)
• VoiceOver and Keyboard Accessibility
• Internationalization and Right to Left layouts
• Different resolutions (1x, 2x, 3x)
• Size classes and window sizes (iPhone vs iPad, notched devices, multitasking, different window sizes, etc)
• iPad Pointer interaction
• SwiftUI consumption (validation or new demo scenarios needed)
• Objective-C exposure (provide it only if needed)

Microsoft Reviewers: Open in CodeFlow