[tests] add BlockedFieldMatrix to tests

.gitsuper

dune/xt/la/algorithms/qr.hh

dune/xt/la/algorithms/triangular_solves.hh

dune/xt/la/container/matrix-interface.hh

dune/xt/la/eigen-solver/internal/base.hh

dune/xt/la/test/eigensolver.hh

...est/eigensolver_for_real_matrix_with_distinct_real_evs.py

...lver_for_real_matrix_with_real_evs_from_3d_pointsource.py

...est/matrixinverter_for_real_matrix_from_3d_pointsource.py