Suppose solving Stokes flow. Suppose storing the Jacobian as a BlockArray as in e.g. Incompressible Navier-Stokes equations via DifferentialEquations.jl · Ferrite.jl (deliberately omitting the non-linear convective term here for simplicity). What is required to instruct LinSolve to perform Schur complement preconditioning (or any other type of segregated solve as preconditioner)? Use case is Navier-Stokes with chemistry for instance.