IBus requires XAUTHORITY and XDG_RUNTIME_DIR to be able to spawn its XIM
implementation correctly. Using launch context to get environment can correctly
launch on non-systemd setups.
Closes: #6998
Signed-off-by: xiaofan <xiaofan@iscas.ac.cn>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2947>