hostip: make 'localhost' return fixed values

hostip: make 'localhost' return fixed values

Resolving the case insensitive host name 'localhost' now returns the
addresses 127.0.0.1 and (if IPv6 is enabled) ::1 without using any
resolver.

This removes the risk that users accidentally resolves 'localhost' to
something else. By making sure 'localhost' is always local, we can
assume a "secure context" for such transfers (for cookies etc).

Closes #7039