Implement basic support of SystemSaveData and Cleanup IFileSystemProxy (#767)

* Implement basic support of SystemSaveData and Cleanup IFileSystemProxy

- Implement `OpenSystemSaveData` as a `IFileSystem` in `SaveHelper`:
  On real device, system saves data are stored encrypted, and we can't create an empty system save data for now. That's why if a user put his own dump of system save in `RyuFs\nand\system\save\`, we extract content in associated folder and open it as a `IFileSystem`. If the system save data don't exist, a folder is created.

- Cleanup `IFileSystemProxy` by adding a Helper class.

- Implement `GetSavePath` in `VirtualFileSystem` and remove `GetGameSavePath` in `SaveHelper`.

* remove the forgotten I

* Fix align

Ryujinx.HLE/FileSystem/SaveInfo.cs

@@ -4,25 +4,24 @@ namespace Ryujinx.HLE.FileSystem
 {
     struct SaveInfo
     {
-        public ulong   TitleId { get; private set; }
-        public long    SaveId  { get; private set; }
-        public UInt128 UserId  { get; private set; }
-
+        public ulong        TitleId      { get; private set; }
+        public long         SaveId       { get; private set; }
         public SaveDataType SaveDataType { get; private set; }
         public SaveSpaceId  SaveSpaceId  { get; private set; }
+        public UInt128      UserId       { get; private set; }
 
         public SaveInfo(
             ulong        titleId,
             long         saveId,
             SaveDataType saveDataType,
-            UInt128      userId,
-            SaveSpaceId  saveSpaceId)
+            SaveSpaceId  saveSpaceId,
+            UInt128      userId = new UInt128())
         {
             TitleId      = titleId;
-            UserId       = userId;
             SaveId       = saveId;
             SaveDataType = saveDataType;
             SaveSpaceId  = saveSpaceId;
+            UserId       = userId;
         }
     }
-}
+}