feat(nix/buildGo): add the import position to errmsg r/2535

When a foreign dep is missing a dependency, it is good to have a
context.

e.g. the `github.com/charmbracelet/bubblegum` package has a lot of
dependencies that are only used in its `examples/` dir; this is not
obvious, unless we also print where the imports come from.

New error message:

```
error: missing foreign dependency 'github.com/containerd/console' in 'github.com/charmbracelet/bubbletea, imported at /nix/store/0cry4sg6bzxqwk5zl2nxhas6k5663svg-source/tea.go:22:2'
```

Change-Id: If34a3c62b9d77d4aea108b5e011e16fbd03e8554
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2852
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

0 files changed, 0 insertions, 0 deletions