Automatic derivation on the backend side for extracted data types

[RaitoBezarius]

Lean supports automatic derivation of Repr and potential other typeclasses, it seems cheap to derive them.

Question is: are there situations where a user doesn't want additional typeclasses attached to their extracted data types?

[RaitoBezarius]

cc @R1kM @sonmarcho

[sonmarcho]

For now I don't see situations where a user seriously doesn't want additional typeclasses, so I suggest we implement this. The real questions is: which typeclasses do we want?
Also, are there situations where Lean will fail to derive the typeclasses?