step-22 uses extractors for the matrix but not for the right hand side

[bangerth]

That's a shame, because step-22 is one of the often used tutorial programs to introduce how we conceptually think about vector-valued problems. Specifically, we should just re-write this block of code:

      const unsigned int component_i =
        fe.system_to_component_index(i).first;
      local_rhs(i) += (fe_values.shape_value(i, q)   // (phi_u_i(x_q)
                       * rhs_values[q](component_i)) // * f(x_q))
                      * fe_values.JxW(q);            // * dx

[peterrum]

This does not seem urgent.