Allow :info for (~) in GHCi

`(~)` is not an identifier according to GHC's parser, which
is why GHCi's `:info` command wouldn't work on it. To rectify this,
we apply the same fix that was put in place for `(->)`: add `(~)` to
GHC's `identifier` parser production.

Test Plan: make test TEST=T10059

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, mpickering, carter

GHC Trac Issues: #10059

Differential Revision: https://phabricator.haskell.org/D4877