client-conf: Check XDG_SESSION_TYPE
If systemd is in use, the XDG_SESSION_TYPE will probably be set (usually to "wayland", "x11", or "tty"). If XDG_SESSION_TYPE is set to something other than "wayland", connect to the X11 server to request properties.
Commit 79a8efb4 stopped connecting to the X server unless SSH_CONNECTION is set in the environment, to avoid launching a useless xwayland process. However, there are many more circumstances in which a remote X server may be in use. For example, XDMCP or VNC.
This does not completely fix #1412, but it does improve the situation.
This is an alternative to !760