[Draft] WIP: FluentButtonStyle

[mischreiber]

Platforms Impacted

• [x] iOS
• [ ] visionOS
• [ ] macOS

Description of changes

Draft implementation of SwiftUI Button, resurrecting some logic from fluent2_tokens branch (especially the demo controller).

TODO:

• Floating buttons look wrong
• Validate spacing between icon and text
• SwiftUI demo controller should have proper theme swapping (via toolbar dropdown thing)
• How do we modify tokenSet on a specific instance? Do we need a tokenSetOverride view modifier? How would that work with a ButtonStyle instead of a full View?

Binary change

(how is our binary size impacted -- see https://github.com/microsoft/fluentui-apple/wiki/Size-Comparison)

Verification

(how the change was tested, including both manual and automated tests)

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