an rename CaptionPreview back to SwCaptionPreview

Change-Id: I24d6f2c66f1c2b152b7d625501ea6fe39d2161ae
Reviewed-on: https://gerrit.libreoffice.org/65015
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>