Export symbolSing, SSymbol, and friends (CLC#85)
This implements this Core Libraries Proposal: https://github.com/haskell/core-libraries-committee/issues/85
In particular, it:
- Exposes the
symbolSing
method ofKnownSymbol
, - Exports the abstract
SSymbol
type used insymbolSing
, and - Defines an API for interacting with
SSymbol
.
This also makes corresponding changes for natSing
/KnownNat
/SNat
and
charSing
/KnownChar
/SChar
. This fixes #15183 (closed) and addresses part (2)
of #21568.