Add new `target` fallback for INP event

[tunetheweb]

See: https://chromestatus.com/feature/5143499213242368 (not shipped yet).

We should continue to use our own selector logic where possible as it's more complete (and customizable), but fallback to this one when the node is empty so that can't be used.

[tunetheweb]

I think this will also allow us to close #335

[logaretm]

This would be fantastic! we implemented a workaround via timing window matching which isn't perfect but mitigates this issue to a limited degree.