generate_licensing_bom: Support the new copied_sources metadata

In addition to finding the licensing information for each package's binaries, this will now also process the newly added copied_sources metadata to find the copyright of files directly copied from the package sources.

https://phabricator.apertis.org/T7616

Signed-off-by: Ryan Gonzalez ryan.gonzalez@collabora.com

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Draft because it depends on pkg/debhelper!29 (merged).