build: update to not need _CRT_NONSTDC_NO_DEPRECATE with MSVC

Use non-deprecated CRT function variants on Windows.

- introduce `curlx_fdopen()`, `curlx_close()` and use them. Map them to
  non-deprecated, underscored, CRT functions on Windows.

- replace `close()` uses with either `sclose()` (for sockets) or
  `curlx_close()` (for files).

- map `fileno`, `unlink`, `isatty` to their non-deprecated, underscored,
  versions on Windows.

- tool_dirhie: map `mkdir` to `_mkdir` on Windows.

- easy: use `_strdup()` on Windows, regardless of how `HAVE_STRDUP` is
  set.

- cmake: assume `HAVE_STRDUP` on Windows. To allow dropping a detection
  hack using `_CRT_NONSTDC_NO_DEPRECATE` with MSVC. Windows always has
  `_strdup()` which the code uses, but also needs `HAVE_STRDUP` defined
  to disable curl's own `strdup()` implementation.

- curl_setup.h: drop `_CRT_NONSTDC_NO_DEPRECATE` as no longer necessary.

Closes #20212

lib/memdebug.c

@@ -497,8 +497,7 @@ ALLOC_FUNC
 FILE *curl_dbg_fdopen(int filedes, const char *mode,
                       int line, const char *source)
 {
-  /* !checksrc! disable BANNEDFUNC 1 */
-  FILE *res = fdopen(filedes, mode);
+  FILE *res = CURLX_FDOPEN_LOW(filedes, mode);
   if(source)
     curl_dbg_log("FILE %s:%d fdopen(\"%d\",\"%s\") = %p\n",
                  source, line, filedes, mode, (void *)res);