Add a property to identify iOS apps being run on macOS with Apple Silicon

## Summary

With the introduction of Mac machines with Apple Silicon, iPhone and iPad apps can now be run natively on macOS with no developer changes needed. Currently there's no way to identify such users in the current properties exposed by Amplitude; they show up as using an Apple iPad Pro. Adding some way to identify apps running natively on macOS would be useful in the same way that Amplitude added a way to identify users leveraging Mac Catalyst in #201.

## Motivations

For the same reason it's useful to differentiate or isolate usage data and patterns on iPhone vs iPad, it would be useful to have the same ability to identify users on macOS.