lib: replace `_tcsncpy`/`wcsncpy`/`wcscpy` with `_s` counterparts (Windows)

lib: replace `_tcsncpy`/`wcsncpy`/`wcscpy` with `_s` counterparts (Windows)

Replace:
- curl_sspi: macro `_tcsncpy()` with `_tcsncpy_s()`.
- curlx/fopen: `wcsncpy()` with `wcsncpy_s()`.
- curlx/fopen: `wcscpy()` with `wcscpy_s()`.

Use of the pre-existing functions were safe. This patch aims to use the
recommended Windows CRT functions. Handle errors returned by them. Also
to avoid the compiler warnings silenced via `_CRT_SECURE_NO_WARNINGS`:

```
lib/curl_sspi.c(152): warning C4996: 'wcsncpy': This function or variable may be unsafe. Consider using wcsncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
lib/curlx/fopen.c(161): warning C4996: 'wcsncpy': This function or variable may be unsafe. Consider using wcsncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
lib/curlx/fopen.c(162): warning C4996: 'wcscpy': This function or variable may be unsafe. Consider using wcscpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
lib/curlx/fopen.c(174): warning C4996: 'wcsncpy': This function or variable may be unsafe. Consider using wcsncpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
lib/curlx/fopen.c(175): warning C4996: 'wcscpy': This function or variable may be unsafe. Consider using wcscpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS.
```

Refs:
https://learn.microsoft.com/cpp/c-runtime-library/reference/strncpy-strncpy-l-wcsncpy-wcsncpy-l-mbsncpy-mbsncpy-l
https://learn.microsoft.com/cpp/c-runtime-library/reference/strncpy-s-strncpy-s-l-wcsncpy-s-wcsncpy-s-l-mbsncpy-s-mbsncpy-s-l
https://learn.microsoft.com/cpp/c-runtime-library/security-features-in-the-crt

Cherry-picked from #19581 (in part)
Closes #19589