Sylvain Henry authored Aug 12, 2021 and Marge Bot committed Sep 11, 2021

Before this patch Integer and Natural literals were desugared into "real"
Core in Core prep. Now we desugar them directly into their final ConApp
form in HsToCore. We only keep the double representation for BigNat#
(literals larger than a machine Word/Int) which are still desugared in
Core prep.

Using the final form directly allows case-of-known-constructor to fire
for bignum literals, fixing #20245.

Slight increase (+2.3) in T4801 which is a pathological case with
Integer literals.

Metric Increase:
    T4801
    T11545