Add Convenience Constructor for Vector of Formulas

[AlexandreAmice]

It would be nice to be able to call the following code blobs.

prog = MathematicalProgram()
x = prog.NewContinuousVariables(4, "x")
prog.AddLinearConstraint(x <= np.ones(4))
prog.AddLinearConstraint(x <= 1)
prog.AddLinearConstraint(x == np.ones(4))
prog.AddLinearConstraint(x == 1)

Currently, all four options fail because we don't support vectorized construction of Formula objects (i.e. one gets an error with just x <= np.ones(4)).

Once we have sugar for constructing vectors of Formula, one would also like to add

Binding<LinearConstraint> AddLinearEqualityConstraint(
      const Eigen::Ref<const MatrixX<symbolic::Expression>>& v,
      const Eigen::Ref<const Eigen::MatrixXd>& lb,
      const Eigen::Ref<const Eigen::MatrixXd>& ub)

to MathematicalProgram.

This makes reading code involving MathematicalPrograms easier to read. For example:

prog.AddLinearConstraint(x <= np.ones(4))
prog.AddLinearConstraint(x, -np.inf*np.ones(4), np.ones(4))

The first is nice and easy to read. The second requires me remembering which arguments should be variables vs bound, and noticing that I said AddLinearConstraint (so I have inequalities) vs AddLinearEqualityConstraint.

[jdetweiler1]

Hi! I'd like to work on this issue. I’ll start implementing it today. Let me know if you have any guidance!