Draft: [istl] Use solver registry from istl after upstream fix

Use Dune::SolverTag registry directly. This requires an upstream feature which automatically discards solvers if they don't compile with a given matrix type. This is supposed to work but currently broken. This MR can be merged once the upstream fix is in place.

Issue tracked here: https://gitlab.dune-project.org/core/dune-istl/-/issues/119