Bug description

I used to be able to do:

import { PrismaClientKnownRequestError } from '@prisma/client';

if (!(err instanceof PrismaClientKnownRequestError)) {
    ...
  }

But now the classes are exported as types so we can't use them in instanceof.

Expected behavior

They should be exported as values.

Environment & setup

• Prisma version: 2.12.0