Ryan Scott authored Sep 02, 2020 and Marge Bot committed Sep 04, 2020

The code that converts promoted tuple data constructors to
`IfaceType`s in `GHC.CoreToIface` was using `isTupleDataCon`, which
conflates boxed and unboxed tuple data constructors. To avoid this,
this patch introduces `isBoxedTupleDataCon`, which is like
`isTupleDataCon` but only works for _boxed_ tuple data constructors.

While I was in town, I was horribly confused by the fact that there
were separate functions named `isUnboxedTupleCon` and
`isUnboxedTupleTyCon` (similarly, `isUnboxedSumCon` and
`isUnboxedSumTyCon`). It turns out that the former only works for
data constructors, despite its very general name! I opted to rename
`isUnboxedTupleCon` to `isUnboxedTupleDataCon` (similarly, I renamed
`isUnboxedSumCon` to `isUnboxedSumDataCon`) to avoid this potential
confusion, as well as to be more consistent with
the naming convention I used for `isBoxedTupleDataCon`.

Fixes #18644.