Distinguish between 'deleted' and 'live' filenames when refusing upload for duplicate filename #18671
Description
In #18662, @freakboy3742 said:
At the very least, the error message should highlight that the issue with a "filename already in use" could be a deleted project.
In addition to #17942, we should also update the error message accordingly here.
Good First Issue: This issue is good for first time contributors. If you've already contributed to Warehouse, work on another issue without this label instead. If there is not a corresponding pull request for this issue, it is up for grabs. For directions for getting set up, see our Getting Started Guide.
If you are working on this issue and have questions, feel free to ask them here, in the #pypa-dev chat channel on Libera, the PyPA Discord or on the Discourse.
Screenshot Required: If your pull request makes a visual change, include a screenshot of your update. This helps our team give you feedback faster.