Currently, create_surface_metal forces a Metal backend, regardless of what is requested. This means it is impossible to create a MoltenVK-backed surface in a project using wgpu-native as Vulkan's create_surface_from_view is only accessible using the raw_window_handle based create_surface.

This is a rather severe limitation with the native bindings, as some important features like bindless are not available in naga's MSL backend.

create_surface_metal should be extended to actually support this case.