hostip: move code to resolve IP address literals to `Curl_resolv`

hostip: move code to resolve IP address literals to `Curl_resolv`

The code was duplicated in the various resolver backends.

Also, it was called after the call to `Curl_ipvalid`, which matters in
case of `CURLRES_IPV4` when called from `connect.c:bindlocal`. This
caused test 1048 to fail on classic MinGW.

The code ignores `conn->ip_version` as done previously in the
individual resolver backends.

Move the call to the `resolver_start` callback up to appease test 655,
which wants it to be called also for literal addresses.

Closes https://github.com/curl/curl/pull/4798