REGTESTS: ssl: split the SSL reuse test into TLS 1.2/1.3

REGTESTS: ssl: split the SSL reuse test into TLS 1.2/1.3

QUIC and TLS don't use the same tests because QUIC only supports
TLS 1.3 while SSL tests both TLS 1.2 and 1.3, which complicates
the tests scenarios.

This change extracts the core of the test into a single generic
ssl_reuse.vtci file and creates new high-level tests for TLSv1.2
over TCP, TLSv1.3 over TCP and TLSv1.3 over QUIC, which simply
include this file and set two variables. The test is now cleaner
and simpler.