Implement wrapper over kernel VFS APIs.

[Tropix126]

What's the motivation for this feature?

The PROS kernel maintains a virtual filesystem (VFS) that stubs newlib's filesystem API calls. This allows access to:

• The microsd card's filesystem (if available).
• UNIX-style device access at /dev/.
• The PROS serial driver at /ser/ that manages stdout and stdin.

Describe the solution you'd like

Add an std::fs-style API for accessing vfs-related things.

Describe the drawbacks, if any

std::fs is a relatively large API surface to re-implement, since it'd also require polyfilling std::path as well. It's certainly doable though.

Describe the alternative solutions, if any

Not sure. Guess you could provide individual implementations for the serial driver and microsd card rather than a filesystem-type approach for everything, but it's probably best to go with that the kernel provides us.

Additional context

https://github.com/purduesigbots/pros/blob/master/src/system/dev/vfs.c