Created by: pvdlg
Currently when navigating a dropdown with the keyboard, in order to determine the current index, this selector is used to find the active elements on the whole document.
All the dropdown-items on the page are retrieved and looped on with a call to item.offsetWidth and item.offsetHeight to determine if they are currently visible.
With this PR the active items are searched only under the parent dropdown.
In addition it avoid the necessity to call item.offsetWidth and item.offsetHeight.
On a side note, the keyboard navigation currently doesn't work in v4 as there is a discrepancy between the html markup (from the documentation) and the javascript. See #19864 for the fix.