bpo-39791: Add files() to importlib.resources (GH-19722)

* bpo-39791: Update importlib.resources to support files() API (importlib_resources 1.5).

* 📜🤖 Added by blurb_it.

* Add some documentation about the new objects added.

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