Zejun Wu authored Jan 21, 2019 and Ben Gamari committed Jan 31, 2019

Summary:
Introduce `GhciMonad`, which is bascially `GhcMonad` + `HasGhciState`.
Generalize the commands and help functions defined in `GHCi.UI` so they
can be used as both `GHCi a` and `InputT GHCi a`.

The long term plan is to move reusable bits to ghci library and make it
easier to build a customized interactive ui which carries customized state
and provides customized commands.

Most changes are trivial in this diff by relaxing the type constraint or
add/remove lift as necessary. The non-trivial changes are:

* Change `HasGhciState` to `GhciMonad` and expose it.
* Implementation of `reifyGHCi`.

Test Plan:
  ./validate

Reviewers: simonmar, hvr, bgamari

Reviewed By: simonmar

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5433