Fix `next/future/image` alt text (#39366)
In many browsers (other than Chrome), the `alt` text is visible while the image is loading. This causes a sense layout shift since you'll see a flash of text and then the image (although lighthouse measures 0 CLS, likely because Chrome doesn't have this problem). This PR updates `next/future/image` to hide the alt text, unless there is an error while loading the image in which case the `alt` text because relevant as the fallback.
Example:
<img width="115" alt="image" src="https://user-images.githubusercontent.com/229881/183128008-0660c50c-18aa-4e64-872e-ada9a652130f.png">
Unfortunately, Safari also shows a border while lazy loading images and it cannot be styled.
See upstream issue here: https://bugs.webkit.org/show_bug.cgi?id=243601
