Building dictionary terms in Core?

[Ömer Sinan Ağacan]

Hi,

In #15646 (recent discussion in Gitlab MR 55) we need dictionary arguments in
Core (in desugarer) to apply to functions like `fromRational :: Fractional a =>
Rational -> a`, but we don't know how to build the dictionary term (`Fractional
a`) in Core. Can anyone who know help us in the MR?

Thanks,

Ömer