Create Environment workspace warning

Observed participant trying to create an environment as prompted in Select Interpreter quick pick and then went through the selection steps and for it to fail at the end because no workspace was open.

It would be nice if we could provide this warning earlier on rather than having the user going through the whole flow and fail in order to be notified

Start by reproducing the environment-creation flow from the Select Interpreter quick pick with no workspace open. Trace where the missing-workspace failure is reported and make the warning appear before the user completes the selection steps; done means the user is notified early instead of reaching the final failure.

Written by the indexing model from the issue text.