HResult::extract_code() is easily confused with HResult::code()

[agashlin]

The documentation should warn that this is probably not what you want, code() being the thing that actually gets the HRESULT, while extract_code returns the same type but masked out.

Unfortunately the generated docs for HResult don't show the methods from the generic ErrorAndSource, there is a link in the summary but it's easy to overlook. I wonder if there is a way to get those included... (looks like this is rust-lang/rust#32077)

Maybe it shouldn't return HRESULT at all, but instead the underlying i32 (same with extract_facility).