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/bufq.h

@@ -214,6 +214,12 @@ bool Curl_bufq_peek_at(struct bufq *q, size_t offset,
  */
 void Curl_bufq_skip(struct bufq *q, size_t amount);
 
+/**
+ * Same as `skip` but shift tail data to the start afterwards,
+ * so that further writes will find room in tail.
+ */
+void Curl_bufq_skip_and_shift(struct bufq *q, size_t amount);
+
 typedef ssize_t Curl_bufq_writer(void *writer_ctx,
                                  const unsigned char *buf, size_t len,
                                  CURLcode *err);