[Re-Introspection] Comments in the schema are removed by re-introspection

## Problem

User-defined comments in a schema are removed with re-introspection. 

```
model user {
  id Int @id
  name String
  type user_type
}

/// Default for a user is NORMAL
enum user_type {
  ADMIN
  NORMAL
}
```

On re-introspection, the comment above the enum is removed

## Suggested solution

The comments should persist after re-introspection