Added CreateFile to the FS_USER service

Tested with hwtests.

src/core/file_sys/archive_backend.h

@@ -199,6 +199,14 @@ public:
      */
     virtual bool DeleteDirectory(const FileSys::Path& path) const = 0;
 
+    /**
+     * Create a file specified by its path
+     * @param path Path relative to the Archive
+     * @param size The size of the new file, filled with zeroes
+     * @return File creation result code
+     */
+    virtual ResultCode CreateFile(const Path& path, u32 size) const = 0;
+
     /**
      * Create a directory specified by its path
      * @param path Path relative to the archive