Implement `org.gtk.Settings` interface
To fix https://bugs.kde.org/show_bug.cgi?id=421745
static const gchar introspection_xml[] =
"<node name='/org/gtk/Settings'>"
" <interface name='org.gtk.Settings'>"
" <property name='FontconfigTimestamp' type='x' access='read'/>"
" <property name='Modules' type='s' access='read'/>"
" <property name='EnableAnimations' type='b' access='read'/>"
" </interface>"
"</node>";