Question: How to add line breaks for every export in ExportNamedDeclaration?

Original contents
```javascript
export {
Foo,
};
```
Recasting
```javascript
const b = recast.types.builders;
const exports = ast.program.body[0];
exports.specifiers = [
...exports.specifiers,
b.exportSpecifier(b.identifier('Bar'), b.identifier('Bar')),
];
ast.program.body = [exports];
console.log(recast.print(ast, {trailingComma: true}).code);
```
Result:
```javascript
export { Foo, Bar };
```
Desired:
```javascript
export {
Foo,
Bar,
};
```

Reproduce the example using recast.types.builders and recast.print with the trailingComma option. Inspect how ExportNamedDeclaration nodes are printed, then define and verify the formatting behavior that produces one specifier per line with a trailing comma.

Written by the indexing model from the issue text.