Use iife format for Rollup

[ankane]

Currently, both esbuild and Webpack output a self-executing function.

(() => {
  // code
})();

This PR updates Rollup to do the same.

(function () {
  // code
})();

With the current es format, Rollup can set a lot of variables and functions on the window object. You can see this with the chart.js package and the following application.js:

import { Chart } from "chart.js/auto"

window.Chart = Chart

With esbuild and Webpack, this only sets an additional Chart variable on window. With Rollup, it sets 400+ more properties.

Object.keys(window).length

[ankane]

Thanks!