Improve from_fn and add com_ptr_from_fn macro

[Osspial]

This PR implements the suggestions I made for from_fn in the Rust Community Discord, with some further iterations. Namely:

• from_fn returns Result<ComPtr<T>, HRESULT> instead of Result<Option<ComPtr<T>>, E>
• F is redefined as FnOnce(&GUID, &mut *mut P) -> HRESULT

It also adds a com_ptr_from_fn function that generalizes from_fn for COM functions that output multiple COM objects (such as ICallFactory::CreateCall).