fdo#70376: Put only document (file) name in window title on OS X

(cherry picked from commit eeb840d6ba930015b969c3d0a98031f0ae508d61)

Change-Id: I0b975a1a0e73c546beec96599fd4e5f87caa51db
Reviewed-on: https://gerrit.libreoffice.org/7838
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>