Without this option `wolfSSL_get_app_data()` always returns NULL.
Disable codepaths using it (and its `set` pair) when curl is built
against a wolfSSL library with this option missing.
Fixing:
```
curl: ../../lib/vtls/wolfssl.c:486: wssl_vtls_new_session_cb: Assertion `cf != ((void *)0)' failed.
```
wolfSSL can be built with the `--enable-context-extra-user-data` or
`-DWOLFSSL_EX_DATA` option to enable this feature. Some higher-level
features also enable it automatically like QUIC, ASIO.
Reported-by: Yedaya Katsman
Bug: https://github.com/curl/curl/pull/19816#issuecomment-3606447845
Ref: https://github.com/curl/curl/actions/runs/19871780796/job/56949160740Closes#19852
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