Create FluentUI_common module, part 1

[mischreiber]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

This is part 1 of creating a new FluentUI_common module to share FluentTheme (and others) between iOS and macOS. The goal of this PR is to rework several files and interfaces in ways that will directly contribute towards the goal of moving this important logic out of the module.

Some highlights of the changes:

• Making many previously internal classes/structures public so the FluentUI_ios module can consume them out of FluentUI_common. For example, much of ControlTokenSet.
• No more TokenizedControlInternal interface. It's been fully folded into TokenizedControl.
• The iOS DynamicColor has been reduced further in importance, and now largely exists only to have something to conform to ShapeStyle for iOS 17.
• Several extensions have been broken up, separating UIKit and SwiftUI logic. The latter of these will often be shared with macOS.
• Move isApplicableThemeChange() onto a UIView extension. This will make it possible to share theme changing logic in the future by creating an equivalent NSView extension.

Binary change

Still working on new system, but when comparing Archive output of the release iOS app:

Before	After
16,755,710	16,792,142

Verification

Key scenario validation pass across iOS demo app.

Visual Verification

Before	After
Screenshot or description before this change	Screenshot or description with this change

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