Exposing/leveraging filesystem features for containers (casefolding, reflinks)

In a discussion during [Container Plumbing Days](https://containerplumbing.org/) 2023, @rhatdan and I got to talking about running Windows applications as Linux containers using Wine. He mentioned that there are filesystem quirks preventing that from working effectively.

In that discussion, I noted that [per-directory casefolding is supported in ext4](https://www.collabora.com/news-and-blog/blog/2020/08/27/using-the-linux-kernel-case-insensitive-feature-in-ext4/) and Wine can use that if available, and it's on the roadmap for Btrfs as well. Additionally, [there's been a proposal and patch to take advantage of reflinks in Wine for space savings](https://www.winehq.org/pipermail/wine-devel/2021-August/193357.html).

That led to him suggesting I open a ticket for exploring how to expose these capabilities in filesystems when applications benefit from them. This particular gap in OCI containers is one of the reasons I wind up using systemd-nspawn instead, so it'd be nice to have this in OCI-based containers too.

cc: @davide125, @josefbacik, @giuseppe