fix(web): popup positioning

Fixes three issues:

* longpress positioning for inlined OSK views where not all elements
  may be in the offset hierarchy; impacts particularly where an inlined
  OSK may be within a flex-box.

* Tweaks position of keytip, to take into account the offsetTop of the
  key element.

* Inverts test for display of longpress callout, matching Keyman 14.