feat: add named export in cjs format file

[zhangyuang]

export default has many bugs when mixed with commonjs, vuex use export default object in vuex.cjs.js which behavior is not like vue-router-next. It cause the below code cannot get correct value in the lastest vite version

import { createStore } from 'vuex'
console.log(createStore === undefined)

[zhangyuang]

vuex.cjs.js export code

[zhangyuang]

vue-router-next export code

[zhangyuang]

cc @kiaking , the problem affect users who used the latest vite in ssr

[haoqunjiang]

FYI, vue-router has named exports in v4 cjs build.
So I think it would be more consistent and intuitive if vuex includes them too.

https://unpkg.com/browse/vue-router@4.0.12/dist/vue-router.cjs.js#L3439
/cc @kiaking