[css-display] Define interaction of display:contents and replaced elements #540
Description
https://drafts.csswg.org/css-display/#box-generation
It was not clear to me from the spec what the expected result of applying display:contents to replaced elements is. The added test for replace contents matches what Gecko implemented.
The implemented behavior seems to be that display:contents on replaced elements and form controls (not all of those are actually replaced elements) is ignored, as far as I can tell.
cc @rune-opera @tabatkins @fantasai