FileSys: add SaveDataArchive

The error checking of SaveDataArchive is completely different from DiskArchive, so it has to be a new class instead of a subclass of DiskArchive.

src/core/CMakeLists.txt

@@ -25,6 +25,7 @@ set(SRCS
             file_sys/disk_archive.cpp
             file_sys/ivfc_archive.cpp
             file_sys/path_parser.cpp
+            file_sys/savedata_archive.cpp
             gdbstub/gdbstub.cpp
             hle/config_mem.cpp
             hle/hle.cpp
@@ -170,6 +171,7 @@ set(HEADERS
             file_sys/file_backend.h
             file_sys/ivfc_archive.h
             file_sys/path_parser.h
+            file_sys/savedata_archive.h
             gdbstub/gdbstub.h
             hle/config_mem.h
             hle/function_wrappers.h