build: drop duplicate include curl/curl.h and others

- curl_range: replace `sendf.h` with direct header dependency
  `curl_trc.h`.
- drop `curl/curl.h` includes from internal sourcees in favor of the
  include made from `curl_setup.h`. Replace it with the latter where
  it's the only include.
- include `curl_setup.h` before using macros, where missing.
- drop redundant `stdlib.h`, `string.h` includes, in favor of
  `curl_setup_once.h` including them.
- drop redundant `limits.h` in favor of `curl_setup.h` including it.
- fake_addrinfo.h: fix typo in comment.
- curl_setup_once.h: drop `stdio.h` in favor of earlier include in
  `curl_setup.h`.
- drop stray, unused, `stddef.h` includes.
- memdebug.h: add missing `stddef.h` include. (relying on accidental
  includes via other headers before this patch.)
- stddef.h: document why it's included.
- strerr: drop `curl/mprintf.h` in favor of `curl/curl.h` including it
  via `curl_setup.h`.

Closes #20027

lib/vssh/libssh.c

@@ -29,8 +29,6 @@
 
 #ifdef USE_LIBSSH
 
-#include <limits.h>
-
 #ifdef HAVE_NETINET_IN_H
 #include <netinet/in.h>
 #endif
@@ -45,7 +43,6 @@
 #include <inet.h>
 #endif
 
-#include <curl/curl.h>
 #include "../urldata.h"
 #include "../sendf.h"
 #include "../hostip.h"

lib/vssh/libssh2.c

@@ -28,8 +28,6 @@
 
 #ifdef USE_LIBSSH2
 
-#include <limits.h>
-
 #ifdef HAVE_NETINET_IN_H
 #include <netinet/in.h>
 #endif
@@ -44,7 +42,6 @@
 #include <inet.h>
 #endif
 
-#include <curl/curl.h>
 #include "../urldata.h"
 #include "../sendf.h"
 #include "../hostip.h"

lib/vssh/vssh.c

@@ -27,7 +27,6 @@
 #ifdef USE_SSH
 
 #include "vssh.h"
-#include <curl/curl.h>
 #include "../curlx/strparse.h"
 #include "../curl_trc.h"
 #include "../escape.h"

lib/vssh/vssh.h

@@ -25,7 +25,7 @@
  ***************************************************************************/
 
 #include "../curl_setup.h"
-#include <curl/curl.h>
+
 #include "../urldata.h"
 
 CURLcode Curl_getworkingpath(struct Curl_easy *data,