week-view: explicitly handle PgUp/PgDown via ShortcutController

ScrolledWindow handles PgUp/PgDown in bubble phase to trigger scrolling.
Which leads to inconsistent behaviour: scrolling when an event is focused,
and moving to the previous/next week when not. Explicitly handling the
shortcuts with a ShortcutController in capture phase makes it consistently
navigate to previous/next week.

Fixes #1409

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/618>

src/gui/views/gcal-week-view.blp

@@ -61,6 +61,22 @@ template $GcalWeekView: Box {
       leave => $on_motion_controller_leave_cb(template) not-swapped;
     }
 
+    // Make the behaviour of Page-Up/Page-Down consistent regardless of
+    // whether an event is selected in the week view.
+    ShortcutController {
+      propagation-phase: capture;
+
+      Shortcut {
+        trigger: "Page_Up";
+        action: "action(win.previous-date)";
+      }
+
+      Shortcut {
+        trigger: "Page_Down";
+        action: "action(win.next-date)";
+      }
+    }
+
     Viewport {
       Box content {
         orientation: horizontal;