Massive performance improvement by using sync requires in NodeJS

Hi everyone,

I've seen a pretty big performance improvement by using sync requires in NodeJS. I just tweaked the `loadOption` function:

```js
if (opts.isNode) {
// import('aaa') => require('aaa')
argPath.parent.callee.type = 'Identifier'
argPath.parent.callee.name = 'require'
}
else {
// import('aaa') => import(/* webpackChunkName: 'aaa-123' */ 'aaa')
argPath.addComment('leading', ` webpackChunkName: '${chunkName}' `)
otherValidMagicComments.forEach(validLeadingComment =>
argPath.addComment('leading', validLeadingComment.value)
)
}
```

It seems like generating multiple chunks, and then using *LimitChunksWebpackPlugin* to merge them all together for SSR is slow. Does my change make sense? Could it break stuff?