Node ESM compatibility issue

When using `dedent` in a node ESM environment, a `import dedent from 'dedent'` statement will result a `{default: dedent}` object.



```

> const dedent = await import('dedent')

undefined

> dedent`abc`

Uncaught TypeError: dedent is not a function

> dedent('abc')

Uncaught TypeError: dedent is not a function

> dedent

[Module: null prototype] {

  __esModule: undefined,

  default: <ref *1> [Function: dedent] { default: [Circular *1] }

}

> dedent.default`abc`

'abc'

```



This issue comes from several reasones: 



1. In `package.json` a `module` filed is specified to `dist/dedent.mjs`, but NodeJS doesn't support this field

2. The `main` field in `package.json` references to `dist/dedent.js` which is a CommonJS module, NodeJS's ESM then transforms `module.exports` into a default export



To address this, we need a `exports` field in `package.json`:



```json

{

  "exports": {

    ".": {

      "types": "./index.d.ts",

      "import": "./dist/dedent.mjs",

      "default": "./dist/dedent.js"

    }

  }

}

```



This will solve the import issue, but is potentially a breaking change to NodeJS ESM environment, would it worse a major version?

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