onRender should support more than a bare function

[cpsievert]

I'd expect this to work, but it currently doesn't:

library(plotly)
library(reactR)

plot_ly() %>%
    onRender(babel_transform("gd => console.log(gd)"))

That's because babel_transform() doesn't return a bare function:

cat(babel_transform("gd => console.log(gd)"))

"use strict";

(function (gd) {
  return console.log(gd);
});

However, HTMLWidgets.evalAndRun assumes we're passing a bare function:

htmlwidgets/inst/www/htmlwidgets.js

Line 236 in 5db27ad

var taskFunc = eval("(" + task + ")");

Seems as though we could support this use case by also trying var taskFunc = eval(task);

[cpsievert]

Closing in favor of the more specific #329