Sufficiently indent match case bodies for other indentation lengths than 4

[cmeeren]

The following is my own style when using 2-space indentation. Note that I indent the case bodies extra to push them past the expressions I match on.

match x with
| Some y ->
    let z = 1
    Some (y + z)
| None -> None

The following is Fantomas with 2-space indentation:

match x with
| Some y ->
  let z = 1
  Some(y + z)
| None -> None

I suggest that Fantomas makes sure to indent the case bodies past the match expressions (e.g. by indenting relative to the start of the case match expression instead of the pipe symbol).

Fantomas already does something similar for lambda bodies:

let a =
  b
  |> List.map (fun (c, h) ->
       let x = 2
       x)

Note how the body is indented relative to List.map, not the pipe symbol.