Fix Notification animation tearing in SwiftUI

[mischreiber]

Platforms Impacted

• iOS
• visionOS
• macOS

Description of changes

Move FluentNotification to use Color instead of UIColor, which resolves the issue with animation tearing in iOS 17.

While developing this fix, I noticed that the animation curve is twice as slow in SwiftUI as in UIKit, so fixed that too.

Binary change

Total increase: 1,608 bytes
Total decrease: -78,792 bytes

File	Before	After	Delta
Total	31,069,608 bytes	30,992,424 bytes	🎉 -77,184 bytes

Full breakdown

File	Before	After	Delta
IndeterminateProgressBar.o	230,320 bytes	231,928 bytes	⚠️ 1,608 bytes
NotificationTokenSet.o	94,216 bytes	94,016 bytes	🎉 -200 bytes
FluentNotification.o	684,792 bytes	663,744 bytes	🎉 -21,048 bytes
__.SYMDEF	4,861,000 bytes	4,837,816 bytes	🎉 -23,184 bytes
UIKit+SwiftUI_interoperability.o	46,664 bytes	12,304 bytes	🎉 -34,360 bytes

Verification

Texted all varieties of notification, in both dark and light mode.

Visual Verification

Before:

before.mp4

After:

after.mp4

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