Add public rnf/hash operations to TypeRep/TyCon

Authored by hvr.

Description

Add public rnf/hash operations to TypeRep/TyCon

Summary:
TyCon and TypeRep are supposed to be abstract, by providing these
additional few public operations the need to import
Data.Typeable.Internal is reduced, and future changes to the internal
structure of TypeRep/TyCon shouldn't require changes in packages such as
deepseq or hashable anymore (hopefully).

Reviewers: ekmett, simonpj, tibbe, austin

Reviewed By: ekmett, simonpj, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D699