Reconstruct a subquery from AST without formatting

I parse a query to an AST and would like to print out one of its child nodes to its original string. I try to use `Unparse(child_node)` but it will format a new string. Is there a way to print its original form?

Here is my basic idea:
```cc
ParseStatement(sql, options.GetParserOptions(), &parser_output)
auto child_node =parser_output->statement()->child(0)->child(0)->child(1);
std::cout << Unparse(child_node); // this method will format the string
```

For example, the original sql is `select * from x join y on x.id = y.id`. And I hope to extract its FROM clause, which should be `x join y on x.id = y.id` in its original form.