Track pointer comparisons

Pointer comparisons are another important way in which a reference to a range-loop variable can be misused. It's _possible_ for Go code to compare two pointers using `==` or `!=`. Although this may not be a very commonly used feature, _someone_ might be using it, so we should check -- it will be interesting to see what we find.

For instance, the below loop will have different semantics after the change. We need to report anywhere we find it.

```
func main() {
var y int
for _, x := range []int{1,2,3,4} {
bar(&x, &y)
}
}

func bar(x, y *int) {
if x == y {
fmt.Printf("memory address %p found before %p", x, y)
}
}
```

Start by locating the existing analysis for references to range-loop variables in this repository. Extend the reported cases to include comparisons using == and !=, using the example in the issue as a behavioral guide, then run the relevant existing analysis checks to confirm such comparisons are reported.

Written by the indexing model from the issue text.