eslint-plugin-next: add ESM named exports via conditional exports field

[12122J]

What?

Add a dual CJS/ESM export setup to @next/eslint-plugin-next so that named ESM imports like import { configs } from '@next/eslint-plugin-next' work correctly.

Fixes #86504.

Why?

SWC compiles TypeScript named exports to CJS using Object.defineProperty() with getter functions:

Object.defineProperty(exports, "configs", { enumerable: true, get: () => configs });

Node.js only creates synthetic ESM named exports from own data properties on module.exports — not accessor (getter) properties. So importing the package via ESM named imports throws:

SyntaxError: Named export 'configs' not found. The requested module
'@next/eslint-plugin-next' is a CommonJS module, which may not support
all module.exports as named exports.

How?

Added a dual-export setup via the package.json "exports" field:

• "require" condition → existing dist/index.js (CJS, no change)
• "import" condition → new dist/index.mjs, a thin ESM wrapper that imports the CJS default and explicitly re-exports the named bindings as data properties:

import cjs from './index.js'
export const { rules, configs } = cjs
export default cjs

dist/index.mjs is generated by scripts/generate-esm.cjs which runs as part of the existing build script after SWC compilation.

After this change:

// ✅ works — ESM named import
import { configs } from '@next/eslint-plugin-next'

// ✅ works — CJS require (unchanged)
const { configs } = require('@next/eslint-plugin-next')

// ✅ works — default import (unchanged)
import plugin from '@next/eslint-plugin-next'