dateMenu: Add "Events" section

Events have a clear and obvious connection to the calendar, and similar
to the Clocks and Weather sections there's a strong link to a particular
application.

Adding them as another section to the right-hand side of the calendar
therefore presents a viable alternative to the old events section.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1282

data/theme/gnome-shell-sass/widgets/_calendar.scss

@@ -177,6 +177,32 @@
   }
 }
 
+/* Events */
+.events-button {
+  @include notification_bubble;
+  padding: $base_padding * 2;
+
+  .events-box {
+    spacing: $base_spacing;
+  }
+
+  .events-list {
+    spacing: 2 * $base_spacing;
+  }
+
+  .events-title {
+    color: desaturate(darken($fg_color,40%), 10%);
+    font-weight: bold;
+    margin-bottom: $base_margin;
+  }
+
+  .event-time {
+    color: darken($fg_color,20%);
+    font-feature-settings: "tnum";
+    @include fontsize($base_font_size - 1);
+  }
+}
+
 /* World clocks */
 .world-clocks-button {
   @include notification_bubble;