search: Fold recurring events into single results

When searching for events, users are typically interested in finding the
event rather than seeing a repetitive list of every occurrence instance.
By configuring the search timelines with "expand-recurrences" set to FALSE,
recurring events are loaded as their single master component instead of
expanding all individual occurrences.

Additionally:
- Update GcalSearchHitEvent subtitle to display "Recurring" (e.g. "Tomorrow • Recurring"
  or "Recurring") when the event has a recurrence rule.
- Safeguard gcal_event_format_date() when running without a default GApplication.

Fixes: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/991
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/808>

src/core/gcal-event.c

@@ -1911,8 +1911,15 @@ gcal_event_format_date (GcalEvent *self)
 
   /* XXX: nasty... */
   application = GCAL_APPLICATION (g_application_get_default ());
-  context = gcal_application_get_context (application);
-  time_format = gcal_context_get_time_format (context);
+  if (application)
+    {
+      context = gcal_application_get_context (application);
+      time_format = gcal_context_get_time_format (context);
+    }
+  else
+    {
+      time_format = GCAL_TIME_FORMAT_24H;
+    }
 
   if (time_format == GCAL_TIME_FORMAT_24H)
     hour_format = "%R";