Previously, rustls was using an on-stack array for TLS data. However,
crustls has an (unusual) requirement that buffers it deals with are
initialized before writing to them. By using calloc, we can ensure the
buffer is initialized once and then reuse it across calls.
Closes#6742
This requires the latest main branch of crustls, which provides
rustls_client_config_builder_dangerous_set_certificate_verifier and
rustls_client_config_builder_set_enable_sni.
This refactors the session setup into its own function, and adds a new
function cr_hostname_is_ip. Because crustls doesn't support verification
of IP addresses, special handling is needed: We disable SNI and set a
placeholder hostname (which never actually gets sent on the wire).
Closes#6719
The Curl_easy pointer struct entry in connectdata is now gone. Just
before commit 215db086e0 landed on January 8, 2021 there were 919
references to conn->data.
Closes#6608
