Replace NativeFile to use SDL IO functions.

[MikuAuahDark]

This removes any platform-specific code from NativeFile and rely on SDL3 IO functions diretly.

One issue I found with this is that SDL3 doesn't expose any function to set the IO buffering mode. This is why this change goes into a PR to discuss how should the buffering function behaves.

[slime73]

Maybe we should make an issue in their repo about this? I feel like it's pretty useful / important, but at the very least we'd get their opinion.

[slime73]

That being said, for now we could probably implement BUFFER_LINE ourselves (like what's done in physfs/File.cpp) and leave the rest as a todo.

[MikuAuahDark]

Alright I opened ticket in SDL for this. libsdl-org/SDL#11832

[MikuAuahDark]

Considering that SDL is just low-level wrapper to OS-specific API (such as Windows file HANDLE or POSIX file descriptor) and there's no explicit way to set buffering mode on those handle/file descriptors, then the best but unfortunate way to solve this is to implement our own buffering.

[MikuAuahDark]

One more thing I forgot to mention is the behavior of file:getSize(). It only returns meaningful values (if applicable) once the file has been opened. If the file is closed, it will always return -1. This is because it uses SDL_GetIOSize which requires valid SDL_IOStream* handle.

[slime73]

Our physfs File backend temporarily opens the file to determine its size in that situation:

love/src/modules/filesystem/physfs/File.cpp

Lines 178 to 184 in f0a7a19

	if (file == nullptr)
	{
	open(MODE_READ);
	int64 size = (int64) PHYSFS_fileLength(file);
	close();
	return size;
	}

[slime73]

Looks good, thanks!