Use shell type API from core to detect shell type

[anthonykim1]

Instead of trying to detect and figure out shell type from extension side: https://github.com/microsoft/vscode-python-environments/blob/main/src/features/common/shellDetector.ts

We should eventually switch over to using terminal shell type from core. Related issue: microsoft/vscode#230165

[flying-sheep]

in #137, I’m adding some type safety to shell type handling.

if we merge that PR before we switch to core APIs, we need to take care to not break its type safe way to make sure all shells are handled in all pieces of the code that handle shells.

[anthonykim1]

Hi @flying-sheep I appreciate you letting me know.
Shell type API (proposed) did get merged just last week, so it may be good idea if we start using it, and hopefully make the shell detection more reliable for activation/deactivation. Though I don't think the list of shell types identically match though.

The goal is I want to lessen the burden so we do less prediction of shell types and environments on extension side of things.
There is also shell environment APIs that are coming up too!

[karthiknadig]

Done via #153