Fix #14135 by validity checking matches

We filter the complete patterns given in a COMPLETE set to only those that
subsume the type we are matching. Otherwise we end up introducing an ill-typed
equation into the overlap checking, provoking a crash. This was the cause of
Trac #14135.

Reviewers: austin, bgamari, mpickering, gkaracha, simonpj, RyanGlScott,
carlostome

Reviewed By: bgamari

Subscribers: carter, dfeuer, RyanGlScott, goldfire, rwbarton, thomie

GHC Trac Issues: #14135

Differential Revision: https://phabricator.haskell.org/D3981