tls: emit `session` after verifying certificate

Prior to this patch `session` event was emitted after `secure` event on
TLSSocket, but before `secureConnect` event. This is problematic for
`https.Agent` because it must cache session only after verifying the
remote peer's certificate.

Connecting to a server that presents an invalid certificate resulted
in the session being cached after the handshake with the server and
evicted right after a certifiate validation error and socket's
destruction. A request initiated during this narrow window would pick
the faulty session, send it to the malicious server and skip the
verification of the server's certificate.

Fixes: https://hackerone.com/reports/811502
CVE-ID: CVE-2020-8172
PR-URL: https://github.com/nodejs-private/node-private/pull/200


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>