Support browsers without IntersectionObserver

I sometimes get error reports from old browsers that lack `IntersectionObserver`. I don't want to ship a polyfill for the small group of users that use these old browsers, I prefer to just show the lazy-loaded content instead.

Would you accept a PR or make the change yourself that makes lazy loaded content visible when `IntersectionObserver` is not available?

Start by locating the lazy-loading component and tracing where IntersectionObserver is checked or used. Verify the fallback behavior in an affected older browser or equivalent test, and consider the work done when lazy-loaded content is visible without IntersectionObserver while current-browser behavior remains unchanged.

Written by the indexing model from the issue text.