[request] better typescript type for `next.config.js` NextConfig

Feature request

Is your feature request related to a problem? Please describe.

i only see this, but any not a good type

declare type NextConfig = any;

if have a type/interface for this we can more easy write a next.config or a config plugin

Describe the solution you’d like

A clear and concise description of what you want to happen.

Describe alternatives you’ve considered

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Additional context

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[eps1lon]

Just leaving my use case here after #8044 was closed without much considerations:

Is your feature request related to a problem? Please describe.

Documentation for config is incomplete and spread out. In-editor autocomplete solves this via types.

Describe the solution you’d like

Export types of next.config.js so that people can use JSDOC to get autcomplete for the config via

/**
 * @type {import('next').Config}
 */
const config = {
  // your config here
};
module.exports = config;

Describe alternatives you’ve considered

Declare the types locally starting from https://github.com/zeit/next.js/blob/287961ed9142a53f8e9a23bafb2f31257339ea98/packages/next/next-server/server/config.ts#L12-L65

[lfades]

This is not one of our current priorities but I’m open to review a PR that adds types for Next.js configurations (similar to #13429 which was closed due to being quite outdated)