RTCCertificateStats: base64Certificate property

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The base64Certificate property of the RTCCertificateStats dictionary is a string containing the base-64 representation of the DER-encoded certificate.

This is essentially an encoding of the original certificate as a string that can safely serialized and deserialized when sent over an IP network.