quic: session.peerCertificate behaves differently than for http2

[martenrichter]

I am currently implementing a custom certificate verifier.
So I wait for the sesssion.opened promise to be fullfilled, and try to check the peerCertificate.
It is an X509Certificate {} object.
I wanted to check the fingerprint256 property. For quic it is a function, for http2 it was a property (supposedly a getter).

The current doc says:

The peer's certificate as an object with properties such as subject, issuer, valid_from, valid_to, fingerprint, etc. Returns undefined if the session is destroyed or the peer did not present a certificate.

So I think the intention is that it is also a property for quic, but it is not.

Also the docu for X509Certificate says:

x509.fingerprint256#
Added in: v15.6.0
Type:
The SHA-256 fingerprint of this certificate.

Though I can see easily what differs between these implementations.
(Of course not a big deal).

@jasnell is this really an issue?

Probably this applies to other properties as well.

[jasnell]

We can make it a getter for quic also.