gtk: add support for the Pause key

Special handing of the Pause key. Implemented in a similar way as in
ui/sdl.c.
Signed-off-by: NMartin Decky <martin@decky.cz>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/gtk.c

@@ -931,6 +931,12 @@ static gboolean gd_key_event(GtkWidget *widget, GdkEventKey *key, void *opaque)
     int qemu_keycode;
     int i;
 
+    if (key->keyval == GDK_KEY_Pause) {
+        qemu_input_event_send_key_qcode(vc->gfx.dcl.con, Q_KEY_CODE_PAUSE,
+                                        key->type == GDK_KEY_PRESS);
+        return TRUE;
+    }
+
     qemu_keycode = gd_map_keycode(s, gtk_widget_get_display(widget),
                                   gdk_keycode);