Handle conflicts when moving files outside unity (diagnostics API)

Here's a case:

- Create a new dir, file and import in Unity.
- Go outside unity, move the file outside the directory.
- Go back to unity and check what happens.
- Now delete the offending directory in Unity.
- Observe we now have an orphan in ~build

May demote this one specific use case but, probably need an option to automatically delete orphans which have a well formed counterpart somewhere else.