Add concatenate_arrays (#717)

* Add merge_temporary_arrays transformation

* type annotate

* move offset computation to a separate loop

* check dependency_names before using map_instructions

* rename

* generate a new array name if not given

* expect a list of args instead of comma separated string of args

* fix flake8 errors

* make mypy's job easier

* Rename, clean up concatenate_arrays

Co-authored-by: Andreas Kloeckner <inform@tiker.net>