curlx: limit use of system allocators to the minimum possible

Clone a multibye conversion function into curlx/fopen, and use that
local copy from curlx/fopen functions. Adjust allocators in curlx/fopen
to use curl's in normal builds, and system allocators in TrackMemory
builds to avoid recursion.

This allows to switch curlx/multibyte functions to curl allocators in
all configurations, as they are no longer called by curlx/fopen, and
a recursive call can no longer happen.

After this patch the system allocator is only used in TrackMemory
Windows builds, within curlx `fopen`, `freopen`, `stat` and `open`
functions.

Also:
- test 1, 440, 767: raise allocation limitsto fit the extra allocations
  in Windows Unicode builds.
- replace all uses of `curlx_unicodefree()` macro with `curlx_free()`
  across the codebase.
- curlx/multibyte: delete `curlx_unicodefree()`.
- ldap: join Windows and non-Windows codepaths that became
  identical after moving from `curlx_unicodefree()` to `curlx_free()`.
- vauth: drop a strdup from standard to curl allocator since
  the original allocation is now already done by curl's.
- tool_doswin: drop now superfluous strdup from `FindWin32CACert()`.
- memanalyzer.pm: sync weirdo `calloc` log message with `malloc`'s.

Fixes #19748
Closes #19845

src/tool_doswin.c

@@ -593,11 +593,8 @@ CURLcode FindWin32CACert(struct OperationConfig *config,
 
   res_len = SearchPath(NULL, bundle_file, NULL, PATH_MAX, buf, &ptr);
   if(res_len > 0) {
-    char *mstr = curlx_convert_tchar_to_UTF8(buf);
-    tool_safefree(config->cacert);
-    if(mstr)
-      config->cacert = curlx_strdup(mstr);
-    curlx_unicodefree(mstr);
+    curlx_free(config->cacert);
+    config->cacert = curlx_convert_tchar_to_UTF8(buf);
     if(!config->cacert)
       result = CURLE_OUT_OF_MEMORY;
   }