This works for in all scenarios, whether it be packages being
added/removed, or upgraded, as well as implicit dependencies.
The output has also been vastly improved, indicating the next
steps that need to be done, and for what packages. It's also
explicit which <site>.txt files have been modified and what changes
were made.
Differential Revision: https://phabricator.services.mozilla.com/D249857
ce997bd43b