use go-enry to identify generated, vendored and other types of code

I just discovered [go-enry](https://github.com/go-enry/go-enry), which GitHub is using [in parts of](https://cs.github.com/about/faq) their new code search. It looks like there [may be a bit there](https://pkg.go.dev/github.com/go-enry/go-enry/v2) that would be useful for automatically excluding generated, vendored, and binary files. I don't think they track comment style, so we couldn't replace that, but this other stuff looks useful.