Initial cut of vgo-aware godef

[myitcv]

DO NOT MERGE

Pushing up an initial cut to make godef vgo-aware

To try this out locally:

cd $(go list -f "{{.Dir}}" github.com/rogpeppe/godef)
git fetch origin refs/pull/80/head:pr_80
git checkout pr_80
go install

[myitcv]

Closing this until there is more movement in golang/go#14120 (comment)

[krasi-georgiev]

Hi @myitcv is this still blocked by the thread you linked? (sorry it is too long to read, I am just after code navigation with vgo in vscode which uses this tool)

#83 another issue on the same topic.

[myitcv]

@krasi-georgiev there has been movement... I'll investigate over the weekend.

[krasi-georgiev]

appreciated, thanks!