tls: properly track writeQueueSize during writes

Make writeQueueSize represent the actual size of the write queue
within the TLS socket. Add tls test to confirm that bufferSize
works as expected.

PR-URL: https://github.com/nodejs/node/pull/15791
Fixes: https://github.com/nodejs/node/issues/15005
Refs: https://github.com/nodejs/node/pull/15006


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>