Feature Request

• Yes, I reviewed the contribution guidelines.

Describe your use case and the problem you are facing

I'd like to be able to wp core download a custom WordPress build, an official or custom ClassicPress build, etc using its URL.

Describe the solution you'd like

wp core download https://somesite/build.zip

In this line, if $version is already a URL then use it as $download_url:

And update documentation and tests accordingly