[v1.1.7] Make `hffs` accessible at root-level

[HfFileSystem] Add top level hffs by @lhoestq #3556.

Example:

>>> from huggingface_hub import hffs
>>> with hffs.open("datasets/fka/awesome-chatgpt-prompts/prompts.csv", "r") as f:
...     print(f.readline())
...     print(f.readline())
"act","prompt"
"An Ethereum Developer","Imagine you are an experienced Ethereum developer tasked..."

Full Changelog: v1.1.6...v1.1.7