Add ASWebAuthenticationSession.Callback support

[kay-schecker]

Is your feature request related to a problem? Please describe.

If I wanna use the https scheme and Universal Links on iOS the completionHandler is not called.

• This is related to Issue Unable to Capture Redirect URLs with 'http' or 'https' CallbackUrlScheme on iOS without user interaction #65

Describe the solution you'd like

Apple has deprecated the previous initializer matching in favor of the new initializer factory functions:

• ASWebAuthenticationSession.Callback.customScheme(String)
• ASWebAuthenticationSession.Callback.https(host: String, path: String)

[ThexXTURBOXx]

Sadly, my MacOS VM is not working properly anymore, so I cannot work on this issue without blindly replacing things. If you have access to Apple hardware (or a VM), feel free to contribute via PR! :)