No support for polymorphism over record fields

My simplex demo needs an ```Eq``` instance for a particular record type. I managed to make one by hand, but is it possible in the current codebase to make a generic constructor of ```Eq``` or other typeclasses for records?

For example, here's the instance for ```Eq``` for pairs:
```
@instance
def pairEq (eqA: Eq a)?=> (eqB: Eq b)?=> : Eq (a & b) = MkEq $
\(x1,x2) (y1,y2). x1 == y1 && x2 == y2
```

I started trying to write an analogous one for records, but because I can't refer to the names of the fields explicitly (or somehow quantify over them), I think it's impossible.

No file, test, or entry point is named. Start by clarifying whether record-field polymorphism and generic Eq or other typeclass construction are intended language features, then define the expected behavior for records before locating the relevant implementation and tests.

Written by the indexing model from the issue text.