Factor out logic for printing dotcalls

[BinderDavid]

In order to make this work I had to unfold the let while loop once. (Because the calling site removes the surrounding Exp::DotCall constructor)

[BinderDavid]

We should maybe also think about combining this with the prettyprinting logic for case, to generate code like this:

foo(a,b,c).bar(...)
                 .baz(...)
                 .case { Foo(x,y) => z }
                 .bizz(..)

I don't think that is supported yet.