gui: Extend the GcalView interface with a method to redraw the weekday layout

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/822>

src/gui/views/gcal-view.c

@@ -294,3 +294,12 @@ gcal_view_event_activated (GcalView        *self,
 
   g_signal_emit (self, signals[EVENT_ACTIVATED], 0, event_widget);
 }
+
+void
+gcal_view_first_weekday_changed (GcalView *self)
+{
+  g_assert (GCAL_IS_VIEW (self));
+  g_assert (GCAL_VIEW_GET_IFACE (self)->first_weekday_changed != NULL);
+
+  GCAL_VIEW_GET_IFACE (self)->first_weekday_changed (self);
+}

src/gui/views/gcal-view.h

@@ -57,6 +57,8 @@ struct _GcalViewInterface
   GList*             (*get_children_by_uuid)                     (GcalView              *view,
                                                                   GcalRecurrenceModType  mod,
                                                                   const gchar           *uuid);
+
+  void               (*first_weekday_changed)                    (GcalView           *view);
 };
 
 void                 gcal_view_set_date                          (GcalView           *view,
@@ -76,4 +78,6 @@ GDateTime*           gcal_view_get_next_date                     (GcalView
 
 GDateTime*           gcal_view_get_previous_date                 (GcalView              *self);
 
+void                 gcal_view_first_weekday_changed             (GcalView              *self);
+
 G_END_DECLS