This generalizes the `Generic1` typeclass to be of kind `k -> *`, and
this also makes the relevant datatypes and typeclasses in `GHC.Generics`
poly-kinded. If `PolyKinds` is enabled, `DeriveGeneric` derives
`Generic1` instances such that they use the most general kind possible.
Otherwise, deriving `Generic1` defaults to make an instance where the
argument is of kind `* -> *` (the current behavior).

Fixes #10604. Depends on D2117.

Test Plan: ./validate

Reviewers: kosmikus, dreixel, goldfire, austin, hvr, simonpj, bgamari

Reviewed By: simonpj, bgamari

Subscribers: thomie, ekmett

Differential Revision: https://phabricator.haskell.org/D2168

GHC Trac Issues: #10604