am: Implement GetSaveDataSize and ExtendSaveData

These functions come in a pair and are needed by Smash Ultimate, Minecraft, and Skyrim, amongst others.

src/core/file_sys/control_metadata.h

@@ -100,7 +100,7 @@ public:
     std::vector<u8> GetRawBytes() const;
 
 private:
-    RawNACP raw;
+    RawNACP raw{};
 };
 
 } // namespace FileSys