Detecting identifiers in struct declarations and/or arguments to anonymous functions.

The findings in [this issue](https://github.com/github-vet/rangeclosure-findings/issues/127) can be avoided by better static analysis.

Consider the below code.
```go
for _, port := range ports {
wg.Add(1)
go func(p int, wg *sync.WaitGroup) {

done := make(chan struct{})

s.jobChan <- portJob{
open: openChan,
closed: closedChan,
filtered: filteredChan,
ip: host,
port: p,
done: done,
ctx: ctx,
}

<-done
wg.Done()

}(port, wg)
}
```

The static analysis is triggering for one of two reasons:
1) either 'port' is mentioned as the label in a struct
2) or it's finding the use of `port` as an argument to the function in the goroutine ~(I think it's probably this one)~.

Both are false-positives for our purposes so it'd be preferred if the analysis ignored these sorts of examples automatically.