[lazy-img] implement native scrolling

[peterpeterparker]

It would be cool to add the native scrolling (https://www.xda-developers.com/google-chrome-image-lazy-loading-speed-up-page-loading-mobile/) to the deckdeckgo-lazy-img component.

But it would be important too:

• still have the ability to lazyLoad() manually
• if native scrolling would not be possible, to fallback on Intersection Observer method and ultimately if nothing is available, to load the image immediately (already the case)

[peterpeterparker]

Seems its possible to detect according https://web.dev/native-lazy-loading

if ('loading' in HTMLImageElement.prototype) {
  // supported in browser
} else {
  // fetch polyfill/third-party library
}