search-button: Use 'search-changed' signal

It uses a 150ms delay, which helps with reducing the number of
queries we do.

src/gui/gcal-search-button.c

@@ -160,9 +160,8 @@ on_search_finished_cb (GObject      *source_object,
 }
 
 static void
-on_entry_text_changed_cb (GtkEntry         *entry,
-                          GParamSpec       *pspec,
-                          GcalSearchButton *self)
+on_entry_search_changed_cb (GtkSearchEntry   *entry,
+                            GcalSearchButton *self)
 {
   g_autofree gchar *sexp_query = NULL;
   GcalSearchEngine *search_engine;
@@ -355,7 +354,7 @@ gcal_search_button_class_init (GcalSearchButtonClass *klass)
 
   gtk_widget_class_bind_template_callback (widget_class, on_button_clicked_cb);
   gtk_widget_class_bind_template_callback (widget_class, on_focus_controller_leave_cb);
-  gtk_widget_class_bind_template_callback (widget_class, on_entry_text_changed_cb);
+  gtk_widget_class_bind_template_callback (widget_class, on_entry_search_changed_cb);
   gtk_widget_class_bind_template_callback (widget_class, on_popover_closed_cb);
   gtk_widget_class_bind_template_callback (widget_class, on_results_listbox_row_activated_cb);
   gtk_widget_class_bind_template_callback (widget_class, on_results_revealer_child_reveal_state_changed_cb);

src/gui/gcal-search-button.ui

@@ -52,7 +52,7 @@
               <object class="GtkSearchEntry" id="entry">
                 <property name="max-width-chars">0</property>
                 <property name="width-chars">0</property>
-                <signal name="notify::text" handler="on_entry_text_changed_cb" object="GcalSearchButton" swapped="no" />
+                <signal name="search-changed" handler="on_entry_search_changed_cb" object="GcalSearchButton" swapped="no" />
 
                 <child>
                   <object class='GtkShortcutController'>