tls: improve TLSSocket & Server performance

Limit the number of closures created and functions called
throughout the lifecycle of TLSSocket, Server & connect.

PR-URL: #15575
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>