Add `.vscode/` to the list of ways to recognize a project root?

[jennybc]

VS Code and Positron will place files below .vscode/ if the user does certain types of workspace-level configuration. This is not a failsafe way to recognize a project, so it's not quite like .Rproj. But I think it would be a nice addition here.

[krlmlr]

Sure, why not.