curlx_win32_fopen: use `_fsopen()`/`_wfsopen()` with `_SH_DENYNO`

curlx_win32_fopen: use `_fsopen()`/`_wfsopen()` with `_SH_DENYNO`

Replacing `fopen_s()`/`_wfopen_s()`, to allow customizing share mode,
and keep the sharing mode as was with `fopen()`/`_wopen()` earlier and
as used in `_sopen_s()`/`_wsopen_s()`.

The replaced functions used `_SH_SECURE` internally. Otherwise they are
identical to the replacements.

Ref: https://learn.microsoft.com/cpp/c-runtime-library/reference/fsopen-wfsopen

Reported-by: Jay Satiro
Fixes #20155
Ref: #20156
Follow-up to 1e7d0bafc6d25d98ec72ff419df65fda3cf147a7 #19643
Closes #20186