feat: Add getter methods for Scope class

[iKlotho]

The getter methods would allow users to check if a specific tag/context/extra is already set or not. I have a use case like this and I don't want to access the protected members of a class. This PR adds getter methods for the following variables: _tags, _contexts, and _extras. If adding getter methods for _contexts and _extras doesn't make sense, I can remove them; however, I think they will be useful.