change name of next.something and next-data

[AugustinMauroy]

I don't think these names are 100% right.

Because 95% of them are server side code, but not specific to nextjs. For example, it could be integrated with remix or fatsify.

So I think we could review the appointment of the rosters and the structure they are in.

[ovflowd]

I'm +1 renaming these.

We could call them engine.XXX (for next.XXX) and server-data for (next-data)

[AugustinMauroy]

What's done quite a bit too, but that's up to the devs, is to put all that in a lib directory, for example, which is what next.js offers for setting up prisma.