Fix Mac Catalyst build

[T.J. Ross (thomasjross)]

Platforms Impacted

• iOS / Mac Catalyst
• visionOS
• macOS

Description of changes

Fixes compilation of the FluentUI Swift package for Mac Catalyst.

Mac Catalyst compilation regressed after:

• Add custom spring animator for BottomSheetController #2249 introduced the UIUpdateLink-based custom bottom-sheet animator, which is unavailable on Mac Catalyst.
• [macOS] Initial implementation of message bar for macOS #2251 moved the NSFont extensions into the common target behind canImport(AppKit). That condition also succeeds for Mac Catalyst even though the required AppKit font APIs are unavailable there.

This change:

• Excludes the AppKit-specific NSFont extensions from Mac Catalyst.
• Excludes the UIUpdateLink-based SheetAnimator implementation from Mac Catalyst.
• Marks the custom spring animator APIs as unavailable on Mac Catalyst.
• Uses the existing UIViewPropertyAnimator path for bottom-sheet animations on Mac Catalyst.

Existing iOS and visionOS behavior remains unchanged.

Binary change

No meaningful binary-size impact is expected. This change only adjusts platform-specific compilation.

Verification

Verified that the FluentUI scheme builds for the generic Mac Catalyst destination in Release configuration.

Visual Verification

Not applicable; this is a build compatibility change with no intended visual impact.

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)

No changes to appearance, accessibility, localization, layout, pointer interaction, SwiftUI consumption, or Objective-C exposure are expected.

Microsoft Reviewers: Open in CodeFlow

[T.J. Ross (thomasjross)]

One possible follow-up would be to hide the platform conditionals behind a small facade in BottomSheetController. The shared call sites could invoke helpers such as startCustomSpringAnimationIfSupported, setHighFrameRateIdleIfSupported, and completeCustomSpringAnimationIfNeeded, with the Mac Catalyst implementation falling back or doing nothing as appropriate.

That would keep the #if !targetEnvironment(macCatalyst) checks localized around the unsupported animator rather than distributing them through the controller’s animation flow. I kept this PR focused on the minimal build fix, but I could do that refactor maintainers would prefer to include it here.

[Joanna Qu (joannaquu)]

what UIUpdateLink api is unavailable? I see it's available from Mac Catalyst 18+ https://developer.apple.com/documentation/uikit/uiupdatelink

[Joanna Qu (joannaquu)]

Mike Schreiber (@mischreiber) is it worth adding catalyst validation or are we still "unofficially" supporting catalyst

[T.J. Ross (thomasjross)]

what UIUpdateLink api is unavailable? I see it's available from Mac Catalyst 18+ https://developer.apple.com/documentation/uikit/uiupdatelink

I think Apple's documentation is wrong. The header in the Catalyst SDK explicitly marks UIUpdateLink as API_UNAVAILABLE(macCatalyst) and the compiler seems emit an error if it is referenced or constructed.

We could probably rebuild this using CADisplayLink for Catalyst while retaining UIUpdateLink on iOS/visionOS. That feels a bit unnecessary to me based on the Catalyst usage, but open to feedback.