Move providers out of rules_pkg

`PackageFilesInfo` is a very useful construct that many codebases use to define how exactly files should be packaged.
I would like for `rules_img` to consume this provider as well to build layers (in the `image_layer` rule).
However, I don't want to depend on the whole transitive closure of rules_pkg (including rules_python).
Could we agree to move providers to a neutral Bazel module that doesn't have any dependencies?
This way, producers and consumers can easily depend on the provider module.

Tagging @aiuto for comment.