Clear and concise description of the problem

Description

Currently, tsdown generates the exports field in package.json without a strictly defined order. According to Node.js documentation and best practices (Dual Package Hazard prevention), the order of keys in the exports object is significant because Node.js uses the first matching condition.

Proposed Change

Ensure that the generated exports object follows the recommended order:

1. types
2. import
3. require
4. default

Example of desired output:

"exports": {
  ".": {
    "import": "./dist/index.mjs",
    "require": "./dist/index.cjs"
  },
  "./package.json": "./package.json"
},

Current behavior