[css-conditional] [css-contain] `srcset` and `sizes` interaction with container queries

With container queries, the way developers write responsive styles changes from querying the global page for information to querying for a parent with containment for information. This shifts responsive paradigms. One case I can forsee is the need to query the parent for sizing and placement of its children. This includes srcset and sizes for responsive images

See also, the need for cw and ch units: #5888

Would the following be able to work with container queries instead of global queries? (ignore syntax, just trying to show the idea):

<img srcset="elva-fairy-480w.jpg 480w,
             elva-fairy-800w.jpg 800w"
     sizes="container(max-width: 600px) 480px,
            800px"
     src="elva-fairy-800w.jpg"
     alt="Elva dressed as a fairy">

<picture>
  <source container="(max-width: 799px)" srcset="elva-480w-close-portrait.jpg">
  <source container="(min-width: 800px)" srcset="elva-800w.jpg">
  <img src="elva-800w.jpg" alt="Chris standing up holding his daughter Elva">
</picture>

Start with the responsive-images reference linked in the issue and compare its srcset, sizes, and picture examples with the proposed container-query behavior. Review related issue #5888; the work is done when the interaction and required syntax have an agreed specification direction.