EVP: Centralise fetching error reporting

EVP: Centralise fetching error reporting

Instead of sometimes, and sometimes not reporting an error in the
caller of EVP_XXX_fetch(), where the error may or may not be very
accurate, it's now centralised to the inner EVP fetch functionality.
It's made in such a way that it can determine if an error occured
because the algorithm in question is not there, or if something else
went wrong, and will report EVP_R_UNSUPPORTED_ALGORITHM for the
former, and EVP_R_FETCH_FAILED for the latter.

This helps our own test/evp_test.c when it tries to figure out why an
EVP_PKEY it tried to load failed to do so.

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12857)