lib: strndup/memdup instead of malloc, memcpy and null-terminate

- bufref: use strndup
 - cookie: use strndup
 - formdata: use strndup
 - ftp: use strndup
 - gtls: use aprintf instead of malloc + strcpy * 2
 - http: use strndup
 - mbedtls: use strndup
 - md4: use memdup
 - ntlm: use memdup
 - ntlm_sspi: use strndup
 - pingpong: use memdup
 - rtsp: use strndup instead of malloc, memcpy and null-terminate
 - sectransp: use strndup
 - socks_gssapi.c: use memdup
 - vtls: use dynbuf instead of malloc, snprintf and memcpy
 - vtls: use strdup instead of malloc + memcpy
 - wolfssh: use strndup

Closes #12453

lib/http.c

@@ -297,7 +297,6 @@ char *Curl_copy_header_value(const char *header)
 {
   const char *start;
   const char *end;
-  char *value;
   size_t len;
 
   /* Find the end of the header name */
@@ -330,14 +329,7 @@ char *Curl_copy_header_value(const char *header)
   /* get length of the type */
   len = end - start + 1;
 
-  value = malloc(len + 1);
-  if(!value)
-    return NULL;
-
-  memcpy(value, start, len);
-  value[len] = 0; /* null-terminate */
-
-  return value;
+  return Curl_strndup(start, len);
 }
 
 #ifndef CURL_DISABLE_HTTP_AUTH