Fix type for HttpProgress struct

[Boddlnagg]

I just stumbled upon the fact that HttpProgress seems to be the only struct that contains reference types as members (Windows.Foundation.IReference<u64>).

Currently this is projected as *mut windows::foundation::IReference<u64>, but we probably don't want to have a raw pointer here. I think that ComPtr<windows::foundation::IReference<u64>> would be correct (i.e. when we get an instance of that struct, the members have their reference count incremented, and we have to Release() the interfaces when we drop the struct), but I'm not 100% sure.