Add net.dial_tcp_from_host{_or_endpoint} and unify them

[haesbaert]

The main motivation for this is to have sinergy with flags parsing, currently flags for a sockaddr returns a net.Host_Or_Endpoint, but we can't just dial from it since there isn't a variant.

Consider the following:

Options :: struct {
	target: net.Host_Or_Endpoint `args:"pos=0,required" usage:"host:port"`,
}

before :: proc() -> (sock: net.TCP_Socket, err: net.Network_Error) {
	opt: Options

	flags.parse_or_exit(&opt, os.args)
	switch t in opt.target {
	case net.Host:
		sock, err = net.dial_tcp(t.hostname, t.port)
	case net.Endpoint:
		sock, err = net.dial_tcp(t)
	}
	return
}

after :: proc() -> (sock: net.TCP_Socket, err: net.Network_Error) {
	opt: Options

	flags.parse_or_exit(&opt, os.args)
	sock, err = net.dial_tcp(opt.target)
	return
}

For completion, add dial_tcp_from_host() and define the upper functions in terms of the newly added ones, cuts one repeated block, now:

from_hostname_and_port_string is parse + from_host_or_endpoint from_hostname_with_port_override is parse + override + from_host_or_endpoint from_host is to_endpoint + from_endpoint
from_host_or_endpoint is from_endpoint or from_host