build: tidy-up MSVC CRT warning suppression macros

[vszakats]

• curl_setup.h: replace _CRT_SECURE_NO_DEPRECATE with
  _CRT_SECURE_NO_WARNINGS, which seems to be the preferred,
  more recent macro for this. Also syncing with libssh2.
  They are equivalent for curl sources with the supported compilers.
• cmake: stop setting _CRT_SECURE_NO_DEPRECATE globally for examples.
• examples: suppress CRT deprecation warnings on a per-file basis.
  To make it work when compiling examples out of curl's build systems.
  Use _CRT_SECURE_NO_WARNINGS.
• examples: document the functions requiring _CRT_SECURE_NO_WARNINGS.
• examples/block_ip: delete superfluous _CRT_SECURE_NO_WARNINGS.
• examples/block_ip: limit _CRT_NONSTDC_NO_DEPRECATE to MSVC.
• examples/log_failed_transfers: fix to set _CRT_SECURE_NO_WARNINGS
  before headers and limit to MSVC.
• curl_setup.h: document which SDKs support _CRT_NONSTDC_NO_DEPRECATE.

[jay]

Just a reminder that the way MS treats "deprecated" is not the way others do because those functions aren't removed. Also like fopen is "insecure", they're never going to get rid of it, all these C functions that they mark as insecure or deprecated because they don't do exactly what MS wants

[vszakats]

@jay I'm aware, yes. Just trying to map it out what exactly are they suppressing,
figuring out if _CRT_SECURE_NO_DEPRECATE or _CRT_SECURE_NO_WARNINGS
is the "best" (I've made a rounds with this in the past, but it's again a bit inconsistent
between libssh2 and parts of curl), and perhaps review how they are suppressed in
examples (per-source would be more user-friendly, but perhaps not practical if many
of them need the defines).

One thing I found is that the warning messages agree on suggesting _CRT_SECURE_NO_WARNINGS.

[vszakats]

_CRT_SECURE_NO_WARNINGS warnings made visible: https://github.com/curl/curl/actions/runs/19446115443/job/55640968722
_CRT_NONSTDC_NO_DEPRECATE fallouts (partial, for lib): https://github.com/curl/curl/actions/runs/19446535634/job/55642317260?pr=19175

[vszakats]

Ended up going with _CRT_SECURE_NO_WARNINGS, which is the one
settled on at libssh2, and seems to be the more recent macro to use.
I documented most fallouts these macros are silencing, and moved
definitions to each example that needs it, from the CMakeLists.txt.
Also fixed some tiny nits found along the way.