views/dazzling-month-view: Tentatively support wheel scroll

Add a dedicated discrete scroll event controller, and ensure
each event controller handles the right types of events.

src/gui/views/gcal-dazzling-month-view.ui

@@ -5,7 +5,6 @@
 
     <child>
       <object class="GtkEventControllerScroll">
-        <!-- TODO: Kinetic -->
         <property name="flags">vertical|kinetic</property>
         <signal name="scroll-begin" handler="on_scroll_controller_scroll_begin_cb" object="GcalDazzlingMonthView" swapped="no" />
         <signal name="scroll" handler="on_scroll_controller_scroll_cb" object="GcalDazzlingMonthView" swapped="no" />
@@ -14,6 +13,13 @@
       </object>
     </child>
 
+    <child>
+      <object class="GtkEventControllerScroll">
+        <property name="flags">vertical|discrete</property>
+        <signal name="scroll" handler="on_discrete_scroll_controller_scroll_cb" object="GcalDazzlingMonthView" swapped="no" />
+      </object>
+    </child>
+
     <!-- Header -->
     <child type="header">
       <object class="GtkBox">