ByteString exposed to Objective-C / Swift cannot see NSData helper

[JakeWharton]

The Kotlin/Native Objective-C headers only expose things transitively referenced from APIs which are public in the module producing the XCFramework. The ByteStringKt class which only exists for darwin platforms to hold the NSData extension therefore does not get exposed, and cannot even be explicitly exposed since Kotlin won't let you reference that implicit enclosing type.

It would be nice if these platform-specific conversion functions existed on the companion object so that if ByteString is exposed all of the niceties to create one for your platform are available. Doing so requires more granular actual's which just adds to the existing pain for lack of https://youtrack.jetbrains.com/issue/KT-20427/.

Still probably worth doing.