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
