As @dobey says, distributing a copy of widevine seems problematic, but strangely debian appear to have a package doing just that.
I doubt Debian is actually distributing widevine. I don't see any available package for it on Ubuntu 18.04 at least. At most, it's probably in the non-free repository, and is simply a download and extract script, similar to how the flashplugin-installer package works, which downloads the official tarball from Adobe, unpacks into a temporary directory, then copies the plug-in to the destination location. It probably also only does this on x86 for widevine, which likely doesn't require downloading a 2GB ChromeOS recovery, and then extracting from there.