Reformat the code using clang-format

Simon Praetoriusrequested to merge
feature/clang-format into main

This is a proposal to add clang-format to our automatic toolchain. The automatic reformatting is not perfect but I am fine with it.

The scripts are based on a work by Alexander Müller, what he proposed for the dune-tensor repo.

Edited by Simon Praetorius

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