Migrate from Objective-C++ to pure Swift

[alex-vasenin]

Swift 5.9 introduced direct interoperability with C++ without relying on Objective-C as a bridge. That means that we can get rid of Objective-C wrappers and improve performance a bit. Backward compatibility isn't much of problem, since starting from 29.04.2024 apps uploaded to the App Store must be build with Xcode 15.