The img inside a <picture> has to re-run "update the image data" when
nearby <source> elements change, so script-driven swaps of srcset (and
the other dimension/media attributes) actually take effect.
Per the HTML spec, the relevant mutations for an img element include:
"The element's parent is a picture element and a source element that
is a previous sibling has its srcset, sizes, media, type, width or
height attributes set, changed, or removed."
The same applies to source insertion, moving, and removal.
Fixes image loading on https://www.apple.com/mac/
