Following other C-level protocols, this VFS protocol is added to help
abstract away implementation details of the underlying VFS in an efficient
way. As a starting point, the import_stat function is put into this
protocol so that the VFS sub-system does not need to know about every VFS
implementation in order to do an efficient stat for importing files.
In the future it might be worth adding other functions to this protocol.
This VFS component allows to mount a host POSIX filesystem within the uPy
VFS sub-system. All traditional POSIX file access then goes through the
VFS, allowing to sandbox a uPy process to a certain sub-dir of the host
system, as well as mount other filesystem types alongside the host
filesystem.
