Moves the point of adding error context to the net::addr module so that
we have access to the raw address input and can include it in the error
message.
This adds a new "verbose-errors" feature flag to async-std that enables
wrapping certain errors in structures with more context. As an example,
we use it in `fs::File::{open,create}` to add the given path to the
error message (something that is lacking in std to annoyance of many).
