Use separate LooseVersion package?

[effigies]

Based on #3466 it seems like there's scope for multiple projects to do what we've done and end up with mutually incompatible LooseVersions. I can't see a very good reason to be comparing LooseVersions across modules, but even so a single source seems better than many.

I've taken what we did in #3466 and turned it into a package: https://pypi.org/project/looseversion/ (repo: https://github.com/effigies/looseversion)

Should we move to that instead of vendoring it locally?

[ghisvail]

I am surprised nobody had done it yet, tbh. I can picture this being useful to other projects, so you might as well provide it as a separate package.