Fix precedence printing of a->(b##c)

[anmonteiro]

This change makes the formatting of fast pipe nodes reuse the same logic that we use elsewhere to format infix operators.

With this change I hope to mitigate future edge cases that would appear because of this custom fast pipe logic.

[IwanKaramazow]

@anmonteiro can you add an extra test for #2118

 (switch (saveStatus) {
                | Pristine => ""
                | Saved => "Saved"
                | Saving => "Saving"
                | Unsaved => "Unsaved"
                })
              ->str

<div>
 (switch (saveStatus) {
                | Pristine => ""
                | Saved => "Saved"
                | Saving => "Saving"
                | Unsaved => "Unsaved"
                })
              ->str
</div>

blocks->(blocks => {"blocks": blocks})
<div> blocks->(blocks => {"blocks": blocks}) </div>

(state.title == "" ? "untitled" : state.title)->str
<title> ((state.title == "" ? "untitled" : state.title)->str) </title>

ReasonReact.Router.watchUrl(url => Route.urlToRoute(url)->ChangeView->(self.send));
ReasonReact.Router.watchUrl(url => Route.urlToRoute(url)->ChangeView->self.send);

[thangngoc89]

@IwanKaramazow I added a number 4 case on #2118. You might want to check it out

[IwanKaramazow]

Discussed in private, ready!