In the OpenStreetMap editing dialog there is a popover that is used for
the hint "bubble" shown when clicking the lightbulb hint button in text fields
and spinner widgets.
Currently the popover is shown/hidden by setting the "visible" property.
A better alternative (available since GTK+ 3.22) is to use
gkt_popover_popup()/gtk_popover_popdown() to show/hide the popover.
The benefit is that we will then get a subte fade-in/out animation instead of
just abruptly showing/hiding (this is also how it's done internally in
GtkMenuButton when it's using a popover, such as the "Add field" button in the
same dialog).