Migrate Region Interfaces to the Prism.Core

[dansiegel]

Summary

All platforms currently support Region Navigation. The interfaces are mostly duplicates of each other however there is some minor API drift between WPF/Uno <--> Maui/Forms

API Changes

We need to consolidate around a single API definition for the core interfaces. The interfaces should be moved to Prism.Core to ensure that we maintain the same contract from one platform to another.

Intended Use Case

This will simplify docs as all platforms will have the same API. Additionally, this will open up the possibility of sharing ViewModels for Prism apps across Wpf, Uno Platform, Xamarin.Forms and .NET MAUI as this will provide both Region Navigation in addition to the recently migrated Dialog Service.