Move the output related functions to another (sub)module

Currently the scanner has a module to store all the artifacts encountered during the discovery process and it also provides functions to show the result.

It would be nice to move those functions in a dedicated module (e.g., output) in order to separate the responsibilities between the two parts and make some tests to validate the output generated by the various formats.

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Migrated from T2692 (view on Phabricator)