displaystatetracker: Fix default layout-mode

The comment in the DisplayConfig xml says the default is logical: https://gitlab.gnome.org/GNOME/xdg-desktop-portal-gnome/-/blob/8e6e4c858525db57cc4717d78f815a1809fb07fb/data/org.gnome.Mutter.DisplayConfig.xml#L382-384

And as far as I can tell, gnome-control-center also uses logical as the default: https://gitlab.gnome.org/GNOME/gnome-control-center/-/blob/04751aebd693d41dc22376c0b0ab71460b1f857a/panels/display/cc-display-config-dbus.c#L1709

cc @janz