Splitting issue

Hi,

My script is as below. Basically it appears that the daygrid plugin is being imported before the core library as I am getting the following output:

```
Hello 0
application-5a1d12524f6b033311d88050725fe217d18e8e926cc71516632699689f192462.js:26 Error: Please import the top-level fullcalendar lib before attempting to import a plugin.
at vdom.js:3:11
```

```
(async () => {
try {
console.log('Hello 0');
const { Calendar } = await import('@fullcalendar/core');
console.log('Hello 1');
const dayGridPlugin = (await import('@fullcalendar/daygrid')).default;
console.log('Hello 2');

let calendarEl = document.getElementById('calendar');

let calendar = new Calendar(calendarEl, {
plugins: [dayGridPlugin],
firstDay: 1,
contentHeight: "auto",
aspectRatio: 1.5,
startParam: 'start',
endParam: 'end',
showNonCurrentDates: true,
headerToolbar: {
start: 'title',
center: 'prevYear,nextYear',
end: 'today prev,next'
}
});

calendar.render();

} catch (error) {
console.log(error);
}
})();
```

Any suggestions as to how to fix this? Without splitting, all the code is combined into one large file which is severely hurting the performance of my site. I really need to only load external frameworks only at the times I need them using splitting like this.

Thanks,
Neil

Start with the supplied script and its dynamic imports of @fullcalendar/core and @fullcalendar/daygrid, then reproduce the import-order error with code splitting enabled. Trace the generated split modules and their loading order; done means the split build loads the core library before the plugin without combining all external frameworks into one file.

Written by the indexing model from the issue text.