This commit adds a templated overload to `SEqualReducer::operator()`
that accepts a lambda function to update the path of the LHS and RHS
of the comparison.

```c++
// Usage prior to this utility function
if (equal.IsPathTracingEnabled()) {
  const ObjectPathPair& self_paths = equal.GetCurrentObjectPaths();
  ObjectPathPair attr_paths = {self_paths->lhs_path->Attr("value"),
                               self_paths->rhs_path->Attr("value")};
  if (!equal(this->value, other->value, attr_paths)) return false;
} else {
  if (!equal(this->value, other->value)) return false;
}

// Usage after this utility function
if (!equal(this->value, other->value,
           [](const auto& path) { return path->Attr("value"); })) {
  return false;
}
```