Add plugin closed message to plugins_api.

[ronalfy]

Currently, the return is a WP_Error, which is fine. However, the message displays that the plugin could not be found. With our use-case, we're trying to distinguish between third-party plugins and .org plugins. Ideally, the message would be contextual.

I suggest that there are two WP_Error objects we can expect from the API. One if the plugin is missing (and it truly doesn't exist) and one if the plugin has been closed (meaning, it exists, but is closed).

This would benefit our use-case, and I imagine other plugins that need to check programmatically if a plugin has been removed from the repo.

[rafiahmedd]

Is there any plan to implement this?