Duplicate scanner results for rollbacked versions

[eviljeff]

Fixes mozilla/addons#16152

Description

Duplicates scanner results linked to a version when we're rolling it back

Context

I tried to make AbstractScannerResult.duplicate as generic as possible, not knowing what future fields could be added to the models. (I started writing a more generic function that would accept any arbitrary fields as overrides - not just version - but it ended up getting complicated due to foreign keys and it really wasn't worth it given our current use case)

Testing

• Have a version with one or more scanner results
• have 1 newer approved version you can rollback over
• rollback to the version with the scanner results
• see the scanner results are shown in reviewer tools for the newly rolled back version

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.

[diox]

Unfortunately doesn't copy over matched_rules for the results, which is a problem.