Improve the implementation of X509_STORE_CTX_get1_issuer()

Improve the implementation of X509_STORE_CTX_get1_issuer()

It is possible for the stack of X509_OBJECTs held in an X509_STORE_CTX to
have a custom compare function associated with it. Normally (by default)
this uses X509_NAME_cmp(). The X509_STORE_CTX_get1_issuer() function
assumed that it would always be X509_NAME_cmp().

By implementing OPENSSL_sk_find_all() function we can avoid explicitly
using X509_NAME_cmp() in X509_STORE_CTX_get1_issuer().

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14728)