fdo#68546 Add menubar's text color of persona to StyleSettings

Change-Id: I376e0b71b71fdbc2eaf2b10adb7792a841cf9098
Reviewed-on: https://gerrit.libreoffice.org/8711
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>