harmonise logging

[alanz]

We seem to have a number of approaches to logging, spread over haskell-lsp, hie and ghcide.

I think there are two decisions we need to take

a) how and what are we going to log? Tapping into the LSP expectations makes sense, which seems to be to use stderr, which can then be managed per process and per client.

b) Which logging framework will we use? In my mind this should be common across haskell-lsp, ghcide, and hls. And that will drag hie in to match, but it should not necessarily be the driver for the decision.

[alanz]

I spoke to @ndmitchell today, I gather the logger in ghcide is an abstraction, it should be easy to instantiate it with the one already used in haskell-lsp etc.

This still leaves open what the logging policy should be.

[teto]

every message on stderr appears as an error in neovim logs (which kinda makes sense, it's stderr after all) but it makes finding actual errors harder.

[michaelpj]

Superseded by #2492