Move providers out of rules_pkg

[malt3]

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.