Prioritize: use Early Hints for images in embed facades (iframes with srcdoc).

[andyj2022]

On our website we can preload the main image that will be LCP, except in the case of pages whose main image is inside a "facade" (for example, a Youtube video thumbnail), since we use the srcdoc of an iframe, and preloading is useless, because Chrome returns to download it later (does not use the image that was preloaded). This doesn't just affect preloads with Early Hints, but any use of preloads.