Explictly register DBus metatypes for shortcuts
Typically this is done in the KGlobalAccel contstructor, but if ksmserver does not have any shortcuts registered we would fail here.
Testing: in kdeglobals
[KDE Action Restrictions][$i]
action/lock_screen[$i]=false
action/start_new_session[$i]=false
action/switch_user[$i]=false
after a reboot
loginctl lock-session
We still lock, going through this manual shortcut path, but without any other shortcut code run.