bpo-39791 native hooks for importlib.resources.files (GH-20576)

* Provide native .files support on SourceFileLoader.

* Add native importlib.resources.files() support to zipimporter. Remove fallback support.

* make regen-all

* 📜🤖 Added by blurb_it.

* Move 'files' into the ResourceReader so it can carry the relevant module name context.

* Create 'importlib.readers' module and add FileReader to it.

* Add zip reader and rely on it for a TraversableResources object on zipimporter.

* Remove TraversableAdapter, no longer needed.

* Update blurb.

* Replace backslashes with forward slashes.

* Incorporate changes from importlib_metadata 2.0, finalizing the interface for extension via get_resource_reader.

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>