Improve GHCi response to loading and unloading modules
Previously GHCi responded to unloading all modules using :l
with Ok, No modules loaded
. This can be confusing, as what it really does is unload modules.
This MR improves various different interactions with GHCi in order to be more informative about what it does. An example can be seen in the comments below.
Note that this breaks some tooling (notably emacs' haskell-mode) so when this is merged an informative message should be posted via multiple channels to inform maintainers of tools.
Fixes #13869 (closed)