Since commit fd0da9606fd2, we only show the "Open Windows" section
if there are at least two windows. That's another subtle difference
with the overview context menus, but while limiting the section to
a minimum of two windows makes sense where the menu always represents
a running app, it is useful to show the section even for single windows
in the dash/app grid.
Account for both uses cases by adding a corresponding option to the
constructor.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1948>
991d9597e0