Add function:GetDiffOfTwoCameras

Change-Id: I3b3f4e8e18d5970d408adcf0457bfdd4e064e37c
Reviewed-on: https://gerrit.libreoffice.org/11588
Reviewed-by: Kohei Yoshida <libreoffice@kohei.us>
Tested-by: Kohei Yoshida <libreoffice@kohei.us>