Properly no-op deprecations and allow unlisting at the same time in API

[joelverhagen]

There is continued internal success and growing interesting in the deprecation API. I would like to make progress on the public preview.

Spec: https://github.com/NuGet/Engineering/pull/4709

For no-oping deprecations, I opted to not use the entity level change tracking API (e.g. https://stackoverflow.com/a/30235307) since it would mean a lot of changes to our abstractions. I think the current implementation is easier to understand anyway.

Summary of changes:

• Properly no-op package deprecations that have no difference
  • [NuGet.org Bug]: many catalog package details leaves are redundant (duplicate) because of improper deprecation no-oping #9921
• Allow packages to be unlisted or relisted at the same time as deprecation
  • [Deprecation]: Add REST API to deprecate packages #8873 (comment)
• Fix a problem where API deprecations were being audited as via the web UI (incorrect)
• Resolve some minor build warnings due to obsolete APIs and cases with no await in and async method
  • Unrelated but small