Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Follow-up to #2165 and #2168 -- moving our system to treat iOS tokens as the same level of importance as macOS. Both now need to be provided by PlatformThemeProviding.

visionOS continues to be special, and lives on as an add-on to iOS.

Verification

Validated alias tokens load as expected in light and dark modes, and appear in components as expected.

Visual Verification

Dark	Light
	n/a

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