Color-contrast should skip elements behind a non-native modal backdrop

[WilcoFiers]

Spotted this problem here:
https://kanecohen.github.io/modal-vanilla/

Axe-core does not run color-contrast against texts when they are covered by a backdrop op a native HTML <dialog> element. However when you do the same with javascript modal (one that doesn't set aria-hidden=true) the text behind the backdrop is failed for having low contrast when the backdrop is on top of it.