Refactor rename rememberViewModel to be architecture agnostic

[xxfast]

The word ViewModels is a misnomer, and may be confusing if you don't want to implement MVVM. The responsibility of this instance is ultimately up to the developer (a view model, a state-holder, domain or whatever) but the only responsibility of this navigation library is to

1. Makes your instances survive configuration changes (on Android) 🔁
2. Hold on to the instance as long as it is in the backstack 🔗

Hopefullty this name rememberOnRoute will make things more straightforward. Coincidently it mirrors the name rememberRouter