lib: transfer origin and proxy handling

Add `data->state.origin` as the origin the transfer is sending the
current request to/gets the response from. Use it for request specific
properties like authentication, hsts and cookie handling, etc.

Unless talking to a forwarding HTTP proxy (e.g. not tunneling),
`data->state.origin` and `conn->origin` are the same.

With a forwarding HTTP proxy in play, `conn->origin` is set to
`conn->http_proxy.peer` and `conn->bits.origin_is_proxy` (a new bit) is
set.

Remove the connection bits, now replaced with:

* `conn->bits.socksproxy` -> `conn->socks_proy.peer`
* `conn->bits.httpproxy` -> `conn->http_proy.peer`
* `conn->bits.proxy` -> `(conn->socks_proy.peer || conn->http_proy.peer`)
* `conn->bits.tunnel_proxy` -> (`conn->http_proy.peer && !conn->bits.origin_is_proxy`)
* `(conn->bits.httpproxy && !conn->bits.tunnel_proxy)` -> `conn->bits.origin_is_proxy`

Rename `noproxy.[ch]` to `proxy.[ch]`. Move the connection proxy setup
code from `url.c` to `proxy.c`.

Remove `data->info.conn_remote_port` as no one uses it.

Add test_40_02b for a SOCKS connection to a forwarding HTTPS proxy.

Update internal documentation about peers and creds.

Closes #21967

lib/Makefile.inc

@@ -241,7 +241,6 @@ LIB_CFILES =         \
   multi_ev.c         \
   multi_ntfy.c       \
   netrc.c            \
-  noproxy.c          \
   openldap.c         \
   parsedate.c        \
   peer.c             \
@@ -249,6 +248,7 @@ LIB_CFILES =         \
   pop3.c             \
   progress.c         \
   protocol.c         \
+  proxy.c            \
   psl.c              \
   rand.c             \
   ratelimit.c        \
@@ -375,13 +375,13 @@ LIB_HFILES =         \
   multi_ntfy.h       \
   multiif.h          \
   netrc.h            \
-  noproxy.h          \
   parsedate.h        \
   peer.h             \
   pingpong.h         \
   pop3.h             \
   progress.h         \
   protocol.h         \
+  proxy.h            \
   psl.h              \
   rand.h             \
   ratelimit.h        \