Add a SKLottieView to play Lottie animations

[mattleibow]

Description of Change

This is the initial set of views and types needed to play Lottie animations from just a single line of XAML:

<controls:SKLottieView Source="Lottie/trophy.json" />

API Changes

public class SKLottieView : SKAnimatedSurfaceView
{
    public static readonly BindableProperty SourceProperty;
    public static readonly BindableProperty DurationProperty;
    public static readonly BindableProperty ProgressProperty;
    public static readonly BindableProperty IsCompleteProperty;

    public SKLottieView();

    public SKLottieImageSource? Source { get; set; }
    public TimeSpan Duration { get; }
    public TimeSpan Progress { get; set; }
    public bool IsComplete { get; }
}

public class SKLottieImageSource : Element
{
    public bool IsEmpty { get; }
}

public class SKFileLottieImageSource : SKLottieImageSource
{
    public string? File { get; set; }
}

public class SKStreamLottieImageSource : SKLottieImageSource
{
    public Func<CancellationToken, Task<Stream?>>? Stream { get; set; }
}

public class SKUriLottieImageSource : SKLottieImageSource
{
    public Uri? Uri { get; set; }
}

Behavioral Changes

None.

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Updated documentation

[amirvenus]

Is there a way to specify the AssetsFolder path for the png images of the animation?