Use generated param decoders in SHA provider

Use generated param decoders in SHA provider

Refactor the SHA provider's context parameter handling in sha2_prov.c to use
the generated parameter decoder framework.

This change replaces manual parameter lookups using `OSSL_PARAM_locate` and
static `OSSL_PARAM` arrays with generated decoder functions and structs. A new
template, `sha2_prov.inc.in`, is added to create the necessary decoders during
the build.

This simplifies the code, reduces boilerplate, and improves type safety.

Signed-off-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28837)