Refactor preserve eol with trivia

[nojaf]

Suggestion to tackle #390
In essence, we collect information from the F# tokens that are not present in the AST (comments, newlines, keywords, ...) and we use to information in CodePrinter to restore the original behaviour.

[nojaf]

@jindraivanek I've encountered something tricky while inserting newlines that have been found.

F.ex

type C () = 
    let rec g x = h x
    and h x = g x

    member x.P = g 3

We print this in CodePrinter with 2 newlines after the and.

However, those newlines are also found in the tokens. So the test fails like:

  Expected string length 75 but was 77. Strings differ at index 54.
  Expected: "... let rec g x = h x\n    and h x = g x\n\n    member x.P = g 3\n"
  But was:  "... let rec g x = h x\n    and h x = g x\n\n\n\n    member x.P = g 3\n"

This all makes sense but how will be ignore found newlines in the trivia when we are already printing them?

[jindraivanek]

@nojaf I think we need to change sepNln to also get node range as parameter and remove NewLine trivia before (maybe we would also need version of sepNln for after node) that node. That way we only print "extra" newlines from trivia.

[nojaf]

Yeah thought of that as well. However, that could lead to a tricky situation where you have a mix of newlines and comments. Worth investigating though.