Remove SyncRequest from K::Object and create a new K::Session type

This is a first step at fixing the conceptual insanity that is our
handling of service and IPC calls. For now, interfaces still directly
derived from Session because we don't have the infrastructure to do it
properly. (That is, Processes and scheduling them.)
HLE: Move kernel/archive.* to service/fs/
HLE: Rename namespaces to match move & fix initialization order
Service.FS: Do archive registration using IdCode instead of name
Service.FS: Rename FileSys::Archive to ArchiveBackend
Service.FS: Rename FileSys::Directory to DirectoryBackend
Service.FS: Rename FileSys::File to FileBackend
FS.Archive: Clean up treatment of archives and their handles

- Refactor FS::Archive internals to make Archive creation and lifetime
  management clearer.
- Remove the "Archive as a File" hack.
- Implement 64-bit Archive handles.