Golang crypto/tls: expose testingOnlyDidHRR from ConnectionState

It can be useful for a TLS server to know (e.g., to log) whether or not a HelloRetryRequest was performed. An example use case is with the increased adoption of PQC and servers doing HRRs depending on whether the client included the X25519MLKEM768 keyshare or not in the ClientHello. With https://github.com/golang/go/issues/67516, we now get the CurveID exposed (yay), but that only provides the final negotiated keygroup, which could be arrived at with or without an HRR; to debug and troubleshoot connections, being able to e.g., log whether an HRR took place would be useful.

To this end, I'd like to propose to expose testingOnlyDidHRR from the ConnectionState in a similar manner as the CurveID; perpas simply named as DidHRR bool.