At present only primal variables are made available in SemidefiniteProgram(), although the dual variables are typically also provided by backends. This ticket added access to dual (and slack) variables.

Depends on #19072

CC: @sagetrac-srobik @mkoeppe @kiwifb

Component: numerical

Author: Dima Pasechnik

Branch: 572b630

Reviewer: Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/20506