Remember the AvailInfo for each IE
This is another take on https://phabricator.haskell.org/D3844.
This patch removes then need for haddock to reimplement the calculation
of exported names from modules. Instead when renaming export lists ghc
annotates each IE with its exported names.
Haddocks current export logic has caused lots of trouble in the past
(on the Github issue tracker):
Updates haddock submodule.
Reviewers: austin, bgamari, ezyang
Reviewed By: bgamari, ezyang
Subscribers: rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D3864