http2: support HTTP/2 to forward proxies, non-tunneling

- with `--proxy-http2` allow h2 ALPN negotiation to
  forward proxies
- applies to http: requests against a https: proxy only,
  as https: requests will auto-tunnel
- adding a HTTP/1 request parser in http1.c
- removed h2h3.c
- using new request parser in nghttp2 and all h3 backends
- adding test 2603 for request parser
- adding h2 proxy test cases to test_10_*

scorecard.py: request scoring accidentally always run curl
with '-v'. Removed that, expect double numbers.

labeller: added http1.* and h2-proxy sources to detection

Closes #10967

lib/http.h

@@ -260,6 +260,7 @@ Curl_http_output_auth(struct Curl_easy *data,
 /* Decode HTTP status code string. */
 CURLcode Curl_http_decode_status(int *pstatus, const char *s, size_t len);
 
+
 /**
  * All about a core HTTP request, excluding body and trailers
  */
@@ -276,13 +277,41 @@ struct http_req {
  * Create a HTTP request struct.
  */
 CURLcode Curl_http_req_make(struct http_req **preq,
-                            const char *method,
-                            const char *scheme,
-                            const char *authority,
-                            const char *path);
+                            const char *method, size_t m_len,
+                            const char *scheme, size_t s_len,
+                            const char *authority, size_t a_len,
+                            const char *path, size_t p_len);
+
+CURLcode Curl_http_req_make2(struct http_req **preq,
+                             const char *method, size_t m_len,
+                             CURLU *url, const char *scheme_default);
 
 void Curl_http_req_free(struct http_req *req);
 
+#define HTTP_PSEUDO_METHOD ":method"
+#define HTTP_PSEUDO_SCHEME ":scheme"
+#define HTTP_PSEUDO_AUTHORITY ":authority"
+#define HTTP_PSEUDO_PATH ":path"
+#define HTTP_PSEUDO_STATUS ":status"
+
+/**
+ * Create the list of HTTP/2 headers which represent the request,
+ * using HTTP/2 pseudo headers preceeding the `req->headers`.
+ *
+ * Applies the following transformations:
+ * - if `authority` is set, any "Host" header is removed.
+ * - if `authority` is unset and a "Host" header is present, use
+ *   that as `authority` and remove "Host"
+ * - removes and Connection header fields as defined in rfc9113 ch. 8.2.2
+ * - lower-cases the header field names
+ *
+ * @param h2_headers will contain the HTTP/2 headers on success
+ * @param req        the request to transform
+ * @param data       the handle to lookup defaults like ' :scheme' from
+ */
+CURLcode Curl_http_req_to_h2(struct dynhds *h2_headers,
+                             struct http_req *req, struct Curl_easy *data);
+
 /**
  * All about a core HTTP response, excluding body and trailers
  */