fs.mitm: WIP LayeredFS impl (NOTE: UNUSABLE ATM)

Also greatly refactors libstratosphere, and does a lot of other things.
There is a lot of code in this one.

stratosphere/fs_mitm/source/fs_shim.h

@@ -20,6 +20,8 @@ typedef struct {
 Result ipcCopyFromDomain(Handle session, u32 object_id, Service *out);
 
 /* Missing fsp-srv commands. */
+Result fsOpenDataStorageByCurrentProcessFwd(Service* s, FsStorage* out);
+Result fsOpenDataStorageByCurrentProcessFromDomainFwd(Service* s, u32 *out_object_id);
 Result fsOpenDataStorageByDataId(Service* s, FsStorageId storage_id, u64 data_id, FsStorage* out);
 Result fsOpenDataStorageByDataIdFromDomain(Service* s, FsStorageId storage_id, u64 data_id, u32 *out_object_id);