crypto/x509: Make GENERAL_NAME_cmp a total order.

GENERAL_NAME_cmp returned -1 in both directions when the name types
differed, as did ASN1_TYPE_cmp (used for otherName values), and
edipartyname_cmp when the nameAssigner fields differed. This made them
unsuitable for sorting. Instead, order by type first, then by the
type-specific contents, with an absent nameAssigner sorting first.
Which non-NULL inputs compare equal is unchanged.

ASN1_TYPE_cmp now sorts NULL before non-NULL values, so two NULLs
compare equal. This lets X509_ALGOR_cmp drop its special case and also
become a total order, with an absent parameter sorting first. Which
inputs compare equal is unchanged.

The one remaining exception is X509_NAME_cmp's -2 return when a name
cannot be serialized, which cannot happen for unmodified parsed names.

While I'm here, remove NULL checks in GENERAL_NAME_cmp and othername_cmp
that cannot be hit.

Update-Note: ASN1_TYPE_cmp and X509_ALGOR_cmp now return a consistent
ordering. Callers that only compare the result against zero are
unaffected, except that ASN1_TYPE_cmp(NULL, NULL) now returns zero
instead of -1. Callers that checked for a specific non-zero value, such
as -1, should compare against zero instead.

Bug: 565047760
Change-Id: I7d8f98c25fe967afbe6ec518b4012a52b1c5e3ba
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/104768
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Moreno Ambrosin <ambrosin@google.com>