Improve core image handling to support modern images

[adamsilverstein]

• Use correct image engine for image type (Can't select an option from the dropdowns adamsilverstein/modern-images-wp#13)

• Ensure images/feeds use compatible image formats - Improve email compatibility for WebP images adamsilverstein/modern-images-wp#25

[dainemawer]

@adamsilverstein apologies if this comment is not placed in the correct issue / PR but would it be feasible to handle alternative image formats as a query param on the image permalink? You see some CDN's manage it that way:

<img src="https://cdn.com/images/image.jpg?format=webp"> - that way we could still make a request to the image, but perhaps return a webp version in the response as image/webp? Just spit balling!

[adamsilverstein]

I am closing this as "wontfix". We are already working on correctly showing the dropdown selection in the Modern Image Formats plugin and have some improvements to AVIF support detection planned for core.