don't overuse requestAnimationFrame

[SteffenDE]

This ensures that JS.focus works on iOS.

Fixes: #3563
Relates to: #1826

[SteffenDE]

@jonatanklosko you originally reported #1826. Could you please check if this reintroduces an issue for livebook?

{:phoenix_live_view, github: "phoenixframework/phoenix_live_view", branch: "sd-requestAnimationFrame-assets", override: true}

includes the built assets.

[jonatanklosko]

@SteffenDE it appears to be working as expected, though we actually changed the Livebook menu from #1826 to use an overlay, so regression probably wouldn't be noticeable. That said, I checked the example I posted on the issue and it also works as expected, so I think we are good :)