Function IsFieldPath

cpp/src/arrow/type.h:2145–2145

  bool operator!() const { return !Equals(FieldPath{}); }

  bool IsFieldPath() const { return std::holds_alternative<FieldPath>(impl_); }
  bool IsName() const { return std::holds_alternative<std::string>(impl_); }
  bool IsNested() const {
    if (IsName()) return false;