vtls: localization of state data in filters

vtls: localization of state data in filters

 - almost all backend calls pass the Curl_cfilter intance instead of
   connectdata+sockindex
 - ssl_connect_data is remove from struct connectdata and made internal
   to vtls
 - ssl_connect_data is allocated in the added filter, kept at cf->ctx

 - added function to let a ssl filter access its ssl_primary_config and
   ssl_config_data this selects the propert subfields in conn and data,
   for filters added as plain or proxy
 - adjusted all backends to use the changed api
 - adjusted all backends to access config data via the exposed
   functions, no longer using conn or data directly

cfilter renames for clear purpose:

 - methods `Curl_conn_*(data, conn, sockindex)` work on the complete
   filter chain at `sockindex` and connection `conn`.
 - methods `Curl_cf_*(cf, ...)` work on a specific Curl_cfilter
   instance.
 - methods `Curl_conn_cf()` work on/with filter instances at a
   connection.
 - rebased and resolved some naming conflicts
 - hostname validation (und session lookup) on SECONDARY use the same
   name as on FIRST (again).

new debug macros and removing connectdata from function signatures where not
needed.

adapting schannel for new Curl_read_plain paramter.

Closes #9919