* Rework VFS to support creating and writing files and introduce OsFileSystem
OsFileSystem abstracts a directory on the device using the filesystem API.
This also introduces GetEntryType and changes FileExists to use it.
* Implement the Horizon FileSystem APIs using our VFS framework
Horizon provides access to files through its IFileSystem class, we can
closely map this to our vfs::FileSystem class.
* Add support for creating application savedata
This implements basic savedata creation using the OsFileSystem API. The
data is stored in Skyline's private directory is stored in the same
format as yuzu.
- The backing system provides a flexible way to access a a region of
abstract memory.
- It is currently barebones and only has support for reading data but
this will be expanded as necessary.
The current implementations are:
- OsBacking - A backing that abstracts a linux file descriptor
- RegionBacking - A backing that creates a region from a portion of an
existing one
