Migrate to Swift, make it standalone and support macOS and tvOS #458
Description
Audio players on macOS and tvOS currently cannot integrate Spotify. Since the Apple ecosystem moved to Swift, Objective C is also no longer a viable option. Migrate the SDK to Swift, make it standalone so the Spotify app is not required and support macOS and tvOS.
At the moment, developers only have the option to use MusicKit. But there's nothing stopping Spotify from building a standalone framework or library for iOS, tvOS and macOS. Third party developers like me can obviously not build a modern framework for Spotify as we lack the necessary APIs to do so.