Bring setting ciphers with mbedTLS in line with other SSL backends,
to make the curl interface more consistent across the backends.
Now the tls1.3 ciphers are set with the --tls13-ciphers option, when
not set the default tls1.3 ciphers are used. The tls1.2 (1.1, 1.0)
ciphers are set with the --ciphers option, when not set the default
tls1.2 ciphers are used. The ciphers available for the connection
are now a union of the tls1.3 and tls1.2 ciphers.
This changes the behaviour for mbedTLS when --ciphers is set, but
--tls13-ciphers is not set. Now the ciphers set with --ciphers
are combined with the default tls1.3 ciphers, whereas before solely
the ciphers of --ciphers were used.
Thus before when no tls1.3 ciphers were specified in --ciphers,
tls1.3 was completely disabled. This might not be what the user
expected, especially as this does not happen with OpenSSL.
Closes#14384
3f7dc8a404