This PR adds a new LottieSwitch component, which is a cross-platform SwiftUI wrapper for AnimatedSwitch. This PR also adds macOS support to AnimatedSwitch and AnimatedControl, which previously was only available on iOS / tvOS.

Before officially releasing a new version with SwiftUI support, I think it makes sense to complete our migration away from the iOS-only UIKit example app and to the multiplatform SwiftUI example app (and then delete the iOS-only example app).

The only functionality in the iOS / UIKit app that doesn't exist in the multiplatform SwiftUI app is the controls demo that lets you test AnimatedSwitch and AnimatedButton. Will add SwiftUI AnimatedButton in a follow-up when I have a chance.