[!311] Enabling vectorization for arbitrary number of blocks

Merge branch 'feature/blockstructured-vectorization-for-arbitrary-blocksize' into 'master'

ref:extensions/dune-codegen This enables vectorization for arbitrary number of
blocks by manually handling the tail of the vectorized loop. The tail can also
be vectorized, if a smaller vector length fits.

Another approach could be to use padding, but I'm currently not sure how to do
that.

See merge request [extensions/dune-codegen!311]

  [extensions/dune-codegen!311]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/311