Formatter: start long lambda clause body on a new line

[paulcadman]

The following example contains a lambda clause that does not fit onto one line.

f : Nat -> Nat;
f :=
  \ {
    | zero := let foo : Nat := 1;in foo
    | _ := 1
  };

It currently gets formatted to:

f : Nat -> Nat;
f :=
  \ {
    | zero := let
      foo : Nat := 1;
    in foo
    | _ := 1
  };

We should format lambda clause bodies in the same way as function bodies. i.e the body should start on a new line if it is too long to fit on one line:

f : Nat -> Nat;
f :=
  \ {
    | zero :=
      let
        foo : Nat := 1;
      in foo
    | _ := 1
  };