Extract cmake functions dune_project into separate file

Summary

The main cmake functions dune_project and finalize_dune_project are extracted into a separate file, including some macros used internally. The macros will be cleaned up in a separate merge-requests.

Depends on !1030 (merged) !1027 (merged) !1028 (merged)

added buildsystem label

changed the description

added 21 commits

• e6cf5b91...93147a65 - 20 commits from branch master
• 24c5b749 - Extract cmake functions dune_project into separate file

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enabled an automatic merge when the pipeline for 24c5b749 succeeds

canceled the automatic merge

enabled an automatic merge when the pipeline for 24c5b749 succeeds

merged

mentioned in commit 24804e43

mentioned in merge request !957 (closed)