move test `dom-element-scroll.html` from mozilla to wpt
<!-- Please describe your changes on the following line: -->
The test `dom-element-scroll.html` was originally landed on #19127.
It was designed for testing `scrollLeft` and `scrollTop`.
It is not only for servo. I thought I put a wrong place at that time. It should not be under `mozilla`. It's better placed under `wpt`.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/20858)
<!-- Reviewable:end -->
Calling scroll() on an element which is not rendered (by a parent with
display: none) would previously cause a crash. In fact, we should
terminate the algorithm
[https://drafts.csswg.org/cssom-view/#dom-element-scroll] at step 10 in
this situation.
The fix hinges on implementing Element::has_css_layout_box() correctly,
rather than just returning true in all cases as we did previously.
Fixes#19430.
