[fixup][md] Make MD grid geometry constructor backwards-compatible

5 jobs for !2970 with fix/md-gg-compatibility
detached
Status Name Job ID Coverage
  Trigger
manual full-dune-latest-release-clang
manual full-dune-latest-release-gcc
manual full-dune-master-gcc
manual minimal-dune-latest-release-gcc
 
  Downstream Modules
created trigger lecture