socks: use dns filter for resolving

Use a dns connection filter to resolve hostnames where their addresses
are locally resolved and forwarded to the SOCKS proxy.

This makes all improvements, like in #21295 for example, also apply
to socks connections. Curl_resolv() is now only called from a DNS
filter.

(ftp still calls Curl_resolv_blocking() in two places, one of which
 may be replaceable with a DNS filter as well to remove the block, tbd)

Closes #21297

lib/cf-dns.h

@@ -42,7 +42,8 @@ CURLcode Curl_cf_dns_insert_after(struct Curl_cfilter *cf_at,
                                   uint8_t dns_queries,
                                   const char *hostname,
                                   uint16_t port,
-                                  uint8_t transport);
+                                  uint8_t transport,
+                                  bool complete_resolve);
 
 CURLcode Curl_conn_dns_result(struct connectdata *conn, int sockindex);
 CURLcode Curl_cf_dns_result(struct Curl_cfilter *cf);