auth: cleanups

- rename `req->proxyuserpwd` to `req->hd_proxy_auth`
- rename `req->userpwd` to `req->hd_auth`
- rename parameter `proxytunnel` to `is_connect` for Curl_http_output_auth()
- move path+query concatenation into Curl_http_output_auth(), saving an alloc when no auth is in play
- rename `H1_HD_USER_AUTH` into `H1_HD_AUTH`

Closes #21513

lib/http.h

@@ -180,8 +180,9 @@ CURLcode Curl_http_write_resp_hds(struct Curl_easy *data,
  * @param request pointer to the request keyword
  * @param httpreq is the request type
  * @param path pointer to the requested path
- * @param proxytunnel boolean if this is the request setting up a "proxy
- * tunnel"
+ * @param query pointer to the requested query or NULL
+ * @param is_connect boolean if this is a CONNECT request
+ *        (where httpreq is HTTPREQ_GET since there is no HTTPREQ_CONNECT)
  *
  * @returns CURLcode
  */
@@ -190,9 +191,8 @@ CURLcode Curl_http_output_auth(struct Curl_easy *data,
                                const char *request,
                                Curl_HttpReq httpreq,
                                const char *path,
-                               bool proxytunnel); /* TRUE if this is
-                                                     the request setting up
-                                                     the proxy tunnel */
+                               const char *query,
+                               bool is_connect);
 
 /* Decode HTTP status code string. */
 CURLcode Curl_http_decode_status(int *pstatus, const char *s, size_t len);