After these changes, in order to add Darwin bind-mount implementation, one only needs:
* Adjust HasBindMounts definition in mount.go
* Provide implementation in mount_darwin.go
There was no consensus on adding dependency on bindfs, that seems to be the only working solution for bind-mounts on Darwin as of today, in https://github.com/containerd/containerd/pull/8789, that's why the actual implementation is not added in current PR.
As a bonus, Linux FUSE-related code was moved to a separate file and possibly could be reused on FreeBSD, though this needs testing.
Signed-off-by: Marat Radchenko <marat@slonopotamus.org>
