Merge branch 'loopsimd_alignment' into 'master'

ref:core/dune-common\> This MR remerges [!670], which was reverted due to to
much time and memory requirement for looptest. This MR merges the branch again
but with two changes:

-   It adds explicit instantiations to the looptest
-   It changes the default template argument of the alignment to 0, which
    means that it has no impact. In particular, if it is set to 0, rebound
    types have the template argument 0 as well. That reduces the number of
    types for that the tests are compiled and executed.

See merge request [core/dune-common!784]

  [!670]: gitlab.dune-project.org/NoneNone/merge_requests/670
  [core/dune-common!784]: gitlab.dune-project.org/core/dune-common/merge_requests/784