Proposal: Associating pattern synonyms with types

[Matthew Pickering]

Dear devs,

There has been a bit of discussion on #10653 about extending exports
to allow users to associate pattern synonyms with types (just like
ordinary data constructors).

There is a section on the wiki which describes the problem and the
proposed behaviour.

https://ghc.haskell.org/trac/ghc/wiki/PatternSynonyms#Associatingsynonymswithtypes

Any comments would be appreciated before I start the implementation.
Please read all the way to the bottom past the examples as their are a
few sections of clarification which might answer your question.

Matt