Include default dependencies when source file not mentioned in cabal file

[brandonchinn178]

Resolves #1032

Technically, only the first commit is necessary to solve the issue. But I refactored the CabalInfo subsystem to ensure that the former CabalFileNotFound + CabalFileDidNotMention branches used the same logic. Specifically, this change allows refineConfig to be the sole source of truth for defining the Cabal information for both a cabal file not existing and a cabal file not mentioning a source file (previously, this was two different locations: parseCabalInfo was doing it for CabalFileDidNotMention and refineConfig was doing it for CabalFileNotFound).

Test

Add the following Haskell file:

foo =
  unlines $
    hello <> world : ["Line " ++ show x | x <- [10 .. 20]]
  where
    hello = "hello"
    world = " world"

Running ormolu on it formats the same in both cases:

1. The Haskell file is in an empty directory
2. The Haskell file is in a directory with a Cabal file, but it's not mentioned in the Cabal file

[mrkkrp]

Thanks! I merged only the first commit though because I'm not sure about the benefits vs mental cost of the others.

[brandonchinn178]

@mrkkrp Thanks! I do think the refactor is an improvement for overall understandability. e.g. it's a bit confusing IMO for CabalInfo to be different for the same cabal file but different source files. Do you mind if I open a separate PR to discuss that?

[mrkkrp]

CabalInfo could be construed as "Cabal information for this particular module we are formatting". Feel free to open a separate PR though.