Now that we keep precise control over GcalEvent instances, and
can use simple pointer comparisons everywhere, GcalMonthView
implemented its update function as a simple remove + add pair.
The problem is that we're not passing the old event instance,
so removals never actually happen, since the new instance is
not yet available to subscribers.
Pass old event in additio to the new one, and use it where it
makes sense.
Closes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/1073
Right now, comparing dates with gcal_date_time_compare_date() gives
the exact opposite result of when comparing using g_date_time_compare().
As shown by this patch, this was a source of *many* bugs.
Georges Basile Stavracas Neto