Formatting document removes '#if DEBUG' and '#endif'

[mandrolic]

Description

(Punted from Ionide issue ionide/ionide-vscode-fsharp#1246)

Encountered when saving a file in a Fable/Elmish project which has this construct, where parts of a piped expression are switched in when in DEBUG:

Program.mkProgram init update view
|> Program.toNavigable parser setRoute
|> Program.withConsoleTrace
#if DEBUG
|> Program.withHMR
#endif
|> Program.withReact "elmish-app"
#if DEBUG
|> Program.withDebugger
#endif
|> Program.run

When formatting, this gets changed to:

Program.mkProgram init update view
|> Program.toNavigable parser setRoute
|> Program.withConsoleTrace
|> Program.withHMR
|> Program.withReact "elmish-app"
|> Program.withDebugger
|> Program.run

To Reproduce
Steps to reproduce the behaviour:

1. Create a fs file with this code:

let foo = [ 1 ]
            |> List.sort
#if DEBUG
            |> List.rev
#endif
            |> List.sort

2. Execute Format Code, or save the file if format on save is enabled

Expected behaviour
Directives are left untouched

Environment (please complete the following information):

• OS: Win 10 1903
• Ionide version: 4.2.0
• VSCode version: 1.39.1
• dotnet SDK version: 2.2
• mono / .Net Framework version:

Repro code

https://jindraivanek.gitlab.io/fantomas-ui/#?code=DYUwLgBAZg9jEF4IG0IEYIF0CwAoCBhRBAPgHwQAyAlgM5gB0tMATmHgMTVQQAiAogCEAqgHE8xSRHJU6jFiABunEADsAJtwlSiMmvSat2+KUA