Allow TLSv1.3 EC certs to use compressed points

Allow TLSv1.3 EC certs to use compressed points

The spec does not prohib certs form using compressed points. It only
requires that points in a key share are uncompressed. It says nothing
about point compression for certs, so we should not fail if a cert uses a
compressed point.

Fixes #5743

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/6055)