`Go to Definition` of try/catch error/stack doesn't return itself

Repro:

```dart
void foo() {
  try {} catch (error, stackTrace) {
    print('$error, $stackTrace');
  }
}
```

Asking for `Go to Definition` on the reference for either does move you to the actual definition but if you are at the definition then it doesn't return itself.

CC @DanTup @srawlins 