Fix T93960: Asset Catalogs I/O fails with unicode file paths on Windows

On Windows, encode file paths as UTF-16 before trying to open the file
for reading/writing.

This introduces a new class `blender::fstream`, which wraps
`std::fstream` and provides this UTF-16 encoding. This class should also
be used in other areas, like the Alembic importer/exporter.

Manifest Task: T93960

Reviewed By: JacquesLucke

Differential Revision: https://developer.blender.org/D13633

source/blender/blenlib/intern/fileops.cc

@@ -0,0 +1,51 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup bli
+ */
+
+#include "BLI_fileops.hh"
+
+#ifdef WIN32
+#  include "utfconv.h"
+#endif
+
+namespace blender {
+fstream::fstream(const char *filepath, std::ios_base::openmode mode)
+{
+  this->open(filepath, mode);
+}
+
+fstream::fstream(const std::string &filepath, std::ios_base::openmode mode)
+{
+  this->open(filepath, mode);
+}
+
+void fstream::open(StringRefNull filepath, ios_base::openmode mode)
+{
+#ifdef WIN32
+  const char *filepath_cstr = filepath.c_str();
+  UTF16_ENCODE(filepath_cstr);
+  std::wstring filepath_wstr(filepath_cstr_16);
+  std::fstream::open(filepath_wstr.c_str(), mode);
+  UTF16_UN_ENCODE(filepath_cstr);
+#else
+  std::fstream::open(filepath, mode);
+#endif
+}
+
+}  // namespace blender