Plugin Directory: Rejected Plugins slugs need to be changed

[Ipstenu]

When a plugin is rejected, it keeps the slug it had before. That means if someone submits the same plugin three times (not a joke) and we reject the first two, we've blocked out the following slugs from use:

this-plugin-name
this-plugin-name-2

The problem? this-plugin-name-3 should be this-plugin-name

Previously, a rejected plugin was renamed to rejected-this-plugin-name-rejected

Can we restore this functionality?

[Otto42]

In 5460:

Plugin Directory: Add 'rejected' to slugs of rejected plugins. Fixes #2737. Props @SergeyBiryukov

[SergeyBiryukov]

In 7800:

Plugins: On upload, if a previously rejected plugin with the same slug was found, free up the slug and proceed with the upload.

This brings parity between plugins rejected before and after [5460].

See #3864. See #2737.