Consider adding `rootMargin` to the Intersection Observer

Feedback from @surma:

I feel like by default you should add a rootMargin to the IO to trigger the load before something comes into the viewport.

So, rootMargin defaults to “0px 0px 0px 0px”, meaning the intersection will be computed between the root element’s unmodified bounds rectangle and the target’s bounds. This change would be made to https://github.com/GoogleChromeLabs/quicklink/blob/master/src/index.mjs#L21

[aretheregods]

@lukeed @addyosmani I’d be happy to do whatever is needed. I’ll make a PR once I’m done.

Edit: I’m getting a microbundle related jsx error that I need to investigate. Once I fix that, I’ll make a PR.

[addyosmani]

@lukeed Mostly me being overscrupulous 😇

I haven’t measured IO initialization costs so don’t have a good mental model of whether this shift practically changes anything. Let’s move ahead 👍I’ll flag if any concerns can be backed up with data.