Enable toolchain venv in new terminals (#21388)

Fixes part of issue #7808 

> This venv should be the one we automatically activate when opening new
terminals, if the detect_venv setting is on.

Release Notes:

- Selected Python toolchains (virtual environments) are now automatically activated in new terminals.

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>