printers, new-printer-dialog: Handle "Escape" shortcut in ui file

As suggested by Matthijs Velsink, it is much cleaner handling UI
related things in the .ui file.

This is a cleaner version of commit 3f612ab81

Related to !2656, fixing #3086

panels/printers/pp-new-printer-dialog.c

@@ -1338,24 +1338,6 @@ search_entry_activated_cb (PpNewPrinterDialog *self)
                   FALSE);
 }
 
-static gboolean
-on_key_press_event (GtkEventControllerKey *controller,
-                   guint                  keyval,
-                   guint                  keycode,
-                   GdkModifierType        state,
-                   PpNewPrinterDialog    *self)
-{
-  /* Capture Escape key press before it propagates down to the Search Entry,
-   * so the dialog can close on Escape. */
-  if (keyval == GDK_KEY_Escape) {
-    gtk_window_close (GTK_WINDOW (self));
-
-    return GDK_EVENT_STOP;
-  }
-
-  return GDK_EVENT_PROPAGATE;
-}
-
 static void
 search_entry_changed_cb (PpNewPrinterDialog *self)
 {
@@ -1901,7 +1883,6 @@ pp_new_printer_dialog_class_init (PpNewPrinterDialogClass *klass)
 
   gtk_widget_class_bind_template_callback (widget_class, add_cb);
   gtk_widget_class_bind_template_callback (widget_class, cancel_cb);
-  gtk_widget_class_bind_template_callback (widget_class, on_key_press_event);
 
   object_class->dispose = pp_new_printer_dialog_dispose;
   window_class->close_request = pp_new_printer_dialog_close_request;

panels/printers/pp-new-printer-dialog.ui

@@ -33,9 +33,14 @@
       <class name="view"/>
     </style>
     <child>
-      <object class="GtkEventControllerKey">
+      <object class="GtkShortcutController">
         <property name="propagation-phase">capture</property>
-        <signal name="key-pressed" handler="on_key_press_event"/>
+        <child>
+          <object class="GtkShortcut">
+            <property name="trigger">Escape</property>
+            <property name="action">action(window.close)</property>
+          </object>
+        </child>
       </object>
     </child>
     <property name="content">