SecurityPkg/AuthVariableLib: Check SHA-256 OID with ContentInfo present

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4305



Based on whether the DER-encoded ContentInfo structure is present in
authenticated SetVariable payload or not, the SHA-256 OID can be
located at different places.

UEFI specification explicitly states the driver shall support both
cases, but the old code assumed ContentInfo was not present and
incorrectly rejected authenticated variable updates when it were
present.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Signed-off-by: Jan Bobek <jbobek@nvidia.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>