openssl: support session resume with TLS 1.3

Session resumption information is not available immediately after a TLS 1.3
handshake. The client must wait until the server has sent a session ticket.

Use OpenSSL's "new session" callback to get the session information and put it
into curl's session cache. For TLS 1.3 sessions, this callback will be invoked
after the server has sent a session ticket.

The "new session" callback is invoked only if OpenSSL's session cache is
enabled, so enable it and use the "external storage" mode which lets curl manage
the contents of the session cache.

A pointer to the connection data and the sockindex are now saved as "SSL extra
data" to make them available to the callback.

This approach also works for old SSL/TLS versions and old OpenSSL versions.

Reviewed-by: Daniel Stenberg <daniel@haxx.se>

Fixes #3202
Closes #3271