Improve exports of postPlanResolver-related code
`postgraphile/postgraphile/__tests__/schema/v4/defaultOptions.1.export.mjs` contains code like:

```js
function Query_tableSetQuery_plan($parent, args, info) {
  const $select = getSelectPlanFromParentAndArgs12($parent, args, info);
  return connection($select, {
    // nodePlan: ($item) => $item,
    cursorPlan($item) {
      return $item.getParentStep ? $item.getParentStep().cursor() : $item.cursor();
    }
  });
}

// ...

const Query_tableSetQuery_postPlanResolvers = [($connection, $parent, fieldArgs, {
  field
}) => {
  const $orderBy = fieldArgs.getRaw("orderBy");
  const $select = $connection.getSubplan();
  const orderByArg = field.args.find(a => a.name === "orderBy");
  $select.apply(extractEnumExtensionValue(orderByArg.type, "pgSelectApply", $orderBy));
  return $connection;
}];

// ...

export const plans = {
  Query: {

// ...

    tableSetQuery: {
      plan($parent, fieldArgs, info) {
        let $result = Query_tableSetQuery_plan($parent, fieldArgs, info);
        for (const ppr of Query_tableSetQuery_postPlanResolvers) {
          $result = ppr($result, $parent, fieldArgs, info);
        }
        return $result;
      },

// ...

  }
};
```

Ideally we could inline this, and end up with something more like:

```js
export const plans = {
  Query: {
    tableSetQuery: {
      plan($parent, fieldArgs, info) {
        // Call the base plan, and store the result into `$result`
        const $select = getSelectPlanFromParentAndArgs12($parent, args, info);
        let $result = connection($select, {
          // nodePlan: ($item) => $item,
          cursorPlan($item) {
            return $item.getParentStep ? $item.getParentStep().cursor() : $item.cursor();
          }
        });

        // Apply each of the post plan resolvers in an unrolled loop:
        {
          const $orderBy = fieldArgs.getRaw("orderBy");
          const $select = $result.getSubplan();
          const orderByArg = field.args.find(a => a.name === "orderBy");
          $select.apply(extractEnumExtensionValue(orderByArg.type, "pgSelectApply", $orderBy));
          // $result = ... (only if changed)
        }

        return $result;
      },
```