Add a pass to collapse concat operations

Frans Skarmanrequested to merge
collapse_concat into inline_attr

Merging into !553

Author checklist

  • New Diagnostics have at least one snapshot test that triggers it
  • Added a changelog entry, if relevant
    • You can use ./add_changelog <MR number or a_descriptive_name> to do this
Edited by Frans Skarman

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