The time direction property tells which orientation one
needs to scroll to change the time of the view. In these
directions (up/down v left/right) the new prev/next
buttons will be pointing.
The two buttons will be added in a subsequent commit,
and will gain view-dependent tooltips.
Signed-off-by: Markus Göllnitz <camelcasenick@bewares.it>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/542>