Merged patch: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Popups/+/644054
Risks: The change should have make no visual difference.
Commit message in full
Reduce layout/style thrashing by measuring all required geometries at event handler, not waiting for delays/redux/style changes.
Use CSS bottom instead of top, to avoid having to measure the popup before positioning it, if it's placed above the link ("flippedY").
Disable some test cases that relied on implementation detail of using "top" CSS.
Smoke test the feature on the beta cluster, looking at multiple page previews on a single page.
QA Results - Beta
QA Results - Prod