We are not allowed to do what we did in #5222 and pass a `NULL` surface
wlr_seat_pointer_notify_enter(), and it's causing crashes when an
xdg-shell popup is active (see #5294 and swaywm/wlroots#2161).
Instead, solve #5220 using the new wlroots API introduced in
swaywm/wlroots#2217.