Create SaveFile() in the FileManagerLoader

[Super-Genius]

You should rename the FIleManagerLoader to just FileManager.

The new void SaveFile(std::string filename, void *data) handlers should follow the LoadFile() handler.

But the filenames could be something like "gpu://dummy.hlsl", which could save the data directly into the gpu or "mnn://test1.mnn", which would save the data to the MNN library