Try setting aspect-ratio on images lacking width and height

[westonruter]

Summary

I started looking at this because I was checking how well Image Prioritizer optimizes a Timber-based theme. It adds fetchpriority=high and lazy-loading correctly, but the Timber starter theme does not include width and height attributes on the featured image, and Image Prioritizer hasn't yet implemented this either. So I wanted to see what it would take.

This experiment tries to set an aspect-ratio on img tags that are missing width and height attributes. There is currently a big problem, however, in that it is setting the aspect-ratio based on the clientBoundingRect and not the intrinsic dimensions of the image. This means that once the aspect-ratio is set the next time that detect.js measures the image, it will use the aspect-ratio for subsequent measurements, meaning that the image dimensions will become locked in place. In order to get around this, I think detect.js may need to be extend to obtain the intrinsic dimensions of elements that have them: img, video, canvas, svg (maybe), and input[type=image] (ewwww).

Another problem is that in order to set the aspect-ratio, the element has to also have width:100% added. This may not be what is intended!

Fixes #10

[westonruter]

Closing since the aspect-ratio approach is not viable. Better to set the width and height attributes on the element to be the corresponding intrinsic dimensions.