Adds a window global for IntersectionObserver support at `Symbol.for("@@support.IntersectionObserver")`.

intersection-support.js

window[Symbol.for("@@support.IntersectionObserver")] = (function(w, k) {
  let y = k.io in w && k.en in w && k.ra in w[k.en][k.pr];
  if (!y) {
    return false;
  }
  if (!(k.ix in w[k.en][k.pr])) {
    Object.defineProperty(w[k.en][k.pr], k.ix, {
      get() {
        return this[k.ra] > 0;
      },
    });
  }
  return true;
})(window, {
  io: "IntersectionObserver",
  en: "IntersectionObserverEntry",
  ra: "intersectionRatio",
  ix: "isIntersecting",
  pr: "prototype"
});