There is currently no support for constructing the classic LP dual of a linear program (LP).
It would be very useful for various reasons, last but not the least constructing certificates of
optimality and of infeasibility of an LP.

CC: @nathanncohen @ppurka

Component: linear programming

Author: Dima Pasechnik

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/13141