The helpers take the active element and body as arguments, so the cases
(focus into the box, keep a control that took focus, restore only when
focus was lost, find the trigger) run under node's test runner.
Opening a popover or a table filter now moves focus into it, closing one
that left focus on nothing puts it back on the trigger, and the triggers
carry aria-haspopup and aria-controls. The shared Popover covers every
caller; the table filter popover, which has its own portal, does the
same.
