Viewing the VsCoq2 server executable and Coq version inside VS Code

[palmskog]

Currently, the user can either specify the path to vscoqtop, or it can be read from path. In the latter case, since many people may have several opam switches, it's not obvious which executable was chosen, and if so, what the corresponding Coq version is.

Therefore, it would be useful to have the executable path and the Coq version (result of vscoqtop --version) displayed somewhere inside VS Code, e.g., in a panel or at least under extension settings. This is not only helpful for users themselves, but also when others are trying to help them debug some problem.

Another related problem, which deserves its own issue, is how to alternate between different opam switches/vscoqtops from inside VS Code.