Can't use Scene::saveToFile() with UTF-8-based string data on Windows

[ParadoxDaKo]

Ramses Version: 27.0.115

For file paths, we are using UTF-8-based strings to support non-ASCII data such as Umlauts or Chinese letters.

Scene::saveToFile() accepts a const char* fileName and essentially passes it to fopen without change/encoding.

A simple const char* literal containing umlauts contains different data as a UTF-8 string with the same umlauts that gets its data passed into a const char* - which fopen doesn't seem to handle properly on Windows systems.

Here is a GTest that elucidates the problem:

TEST(ramses, saveToFile_withUmlauts) {
    ramses::RamsesFramework ramsesFramework;
    ramses::RamsesClient& client = *ramsesFramework.createClient("example client");
    ramses::Scene* scene = client.createScene(ramses::sceneId_t(123u), ramses::SceneConfig(), "export scene");

    std::filesystem::path path("saveToFile_äöü.ramses");	
    auto status = scene->saveToFile(path.generic_u8string().c_str(), false);

    ASSERT_EQ(status, 0);
}

In this test case, Ramses would try and save a file with the filename saveToFile_äöü.ramses.

PS: Even const char* literals with Chinese letters don't work with Scene::saveToFile().