devel/R-cran-S7: new port

An Object Oriented System Meant to Become a Successor to S3 and S4

A new object oriented programming system designed to be a successor to S3 and
S4. It includes formal class, generic, and method specification, and a limited
form of multiple dispatch. It has been designed and implemented collaboratively
by the R Consortium Object-Oriented Programming Working Group, which includes
representatives from R-Core, 'Bioconductor', 'Posit'/'tidyverse', and the wider
R community.