constructor() {
    super(null, null, null);
    this.namedExports = [];
    this.starExports = [];
  }
Visits a parse tree and adds all the exports.

  export {x, y as z};
  export {a, b as c} from 'd'
  export class C {}
  export var v = 1;
  export default 42;
  ...

This extends ExportVisitor but instead of following `export * from 'name'`
it adds the ModuleSpecifier to the starExports.