gdk: quartz: Avoid page up/down getting filtered by gtk_im_context_filter_keypress()

For page up/down events (Fn+up_arrow and Fn+down_arrow on macOS)
gtk_im_context_filter_keypress() currently returns TRUE when im-quartz is
used. This means these events get removed when this function is used
(happens e.g. with the Scintilla text editing library).

Adding scrollPageDown: and scrollPageUp: into GdkQuartzView seems to
resolve the issue as these seem to get called instead of the already
present pageUp: and pageDown:.

gdk/quartz/GdkQuartzView.c

@@ -532,6 +532,20 @@
 		     GUINT_TO_POINTER (GIC_FILTER_PASSTHRU));
 }
 
+-(void)scrollPageDown: (id)sender
+{
+  GDK_NOTE (EVENTS, g_message ("scrollPageDown"));
+  g_object_set_data (G_OBJECT (gdk_window), GIC_FILTER_KEY,
+		     GUINT_TO_POINTER (GIC_FILTER_PASSTHRU));
+}
+
+-(void)scrollPageUp: (id)sender
+{
+  GDK_NOTE (EVENTS, g_message ("scrollPageUp"));
+  g_object_set_data (G_OBJECT (gdk_window), GIC_FILTER_KEY,
+		     GUINT_TO_POINTER (GIC_FILTER_PASSTHRU));
+}
+
 -(void)selectAll: (id)sender
 {
   GDK_NOTE (EVENTS, g_message ("selectAll"));