Revert "Switch dialog/popover to using place-self:dialog" #11975
Description
What is the issue with the HTML Standard?
I looked into reverting #11656 as the CSS-side change did not work out and it seems @tabatkins has forgotten about it, but I don't really understand what's involved.
In particular for the corresponding WPT changes it seems @bfgeek removed some of the test changes in web-platform-tests/wpt@2f10d7c but html/semantics/popovers/popover-alignment-001.htmland html/semantics/popovers/popover-alignment-002.html are still there, were modified by @fantasai, and have multiple passing implementations. If we revert the specification change, what does that mean for popover-alignment-001 and 2?
cc @whatwg/css