Adds a HIP for efficiently mapping files into sandboxes

This covers both the guest binary for the sandbox and arbitrary user mapped files. It proposes a capability that users minimal amounts of memory whilst retaining low overhead, that integrates with sandbox snapshot and restore and paves the way for future snapshot persistence.

Signed-off-by: Simon Davies <simongdavies@users.noreply.github.com>

Author: simongdavies