make conversion of std::filesystem:path to std::string explicit (fix …

…Windows build error)

src/SgfcUtility.cpp

@@ -190,7 +190,7 @@ namespace LibSgfcPlusPlus
   std::string SgfcUtility::GetTempFolderPath()
   {
     std::filesystem::path tempFolderPath = std::filesystem::temp_directory_path();
-    return tempFolderPath;
+    return tempFolderPath.u8string();
   }
 
   std::string SgfcUtility::GetUniqueTempFileName()

src/SgfcUtility.h

@@ -155,8 +155,9 @@ namespace LibSgfcPlusPlus
     /// SgfcPrivateConstants::ArgumentTypeToCmdlineOptionMap.
     static std::string MapArgumentTypeToCmdlineOption(SgfcArgumentType argumentType);
 
-    /// @brief Returns the full path to a folder that is suitable for temporary
-    /// files. The path is guaranteed to exist and to be a directory.
+    /// @brief Returns the full path of a folder that is suitable for temporary
+    /// files. The path is guaranteed to exist and to be a directory. The
+    /// returned path string is UTF-8 encoded.
     ///
     /// The implementation makes use of std::filesystem::temp_directory_path(),
     /// which is defined in C++17 but may not be available on older platform
@@ -182,9 +183,10 @@ namespace LibSgfcPlusPlus
     ///   file
     static std::string GetUniqueTempFileName();
 
-    /// @brief Returns the unique absolute path name of a file that is extremely
+    /// @brief Returns the unique absolute path of a file that is extremely
     /// unlikely to already exist in the temporary folder returned by
-    /// GetTempPath(). This method never returns the same value twice.
+    /// GetTempPath(). The returned path string is UTF-8 encoded. This method
+    /// never returns the same value twice.
     ///
     /// This is a convenience function that invokes JoinPathComponents() using
     /// the return values of GetTempFolderPath() and GetUniqueTempFileName().