Extract "getting files" outside `clobber`
Extract "getting files" outside `clobber`

"getting files" is one of the places that requires files to be on disk.
By extracting this out of `clobber` we can make it simpler and then
trade it out for a zip-based implementation.

pradyunsg/pip,sbidoul/pip,pfmoore/pip,sbidoul/pip,pypa/pip,pypa/pip,pfmoore/pip,pradyunsg/pip