Fix #15331 with careful blasts of parenthesizeHsType

Authored by RyanGlScott on Thu, Jul 5, 7:51 AM.

Description

Fix Trac #15331 with careful blasts of parenthesizeHsType

Another -ddump-splices bug that can be solved with more
judicious use of parentheses.

Test Plan: make test TEST=T15331

Reviewers: goldfire, bgamari, alanz, tdammers

Reviewed By: tdammers

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: Trac #15331

Differential Revision: https://phabricator.haskell.org/D4920

(cherry picked from commit b6a3386186b77333b7a6cdc163499d7dae0dad1c)