Returns the track associated with a specified track identifier.
- iOS 4.0+
- macOS 10.7+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 6.0+
The track identifier of the requested asset track.
The track associated with the track identifier, or nil if no track with the specified identifier is available.
You can call this method without blocking when the data in the
tracks property is already loaded.