Getting "'opts.calledFrom' is unset or empty" even when doing new(std.thisFile)

I have the following lines in a jsonnet file

```
local tanka = import 'github.com/grafana/jsonnet-libs/tanka-util/main.libsonnet';
local helm = tanka.helm.new(std.thisFile);
```

And I'm seeing the `'opts.calledFrom' is unset or empty` warning anyway.

I'm on the latest version (0.4.1), I'm running in Tanka mode, the `chartfile.yaml` file and the `charts/` directory are there, and I have the dependency on https://github.com/grafana/jsonnet-libs.git pointing to `master` in `jsonnetfile.json`.

Also, running `tk show ...` on the command line works fine, both on the integrated terminal and on an external terminal.

Am I missing something? Is there a setting I can configure to make the warning go away?

Reproduce the warning in VS Code 0.4.1 using Tanka mode, the shown jsonnet file, chartfile.yaml, charts/, and jsonnetfile.json, then compare it with tk show in the terminal. Trace how the extension handles tanka.helm.new(std.thisFile) and determine whether a setting or extension change is needed; done means the false warning is removed or its required configuration is documented.

Written by the indexing model from the issue text.