lib: TLS session ticket caching reworked

Described in detail in internal doc TLS-SESSIONS.md

Main points:
- use a new `ssl_peer_key` for cache lookups by connection filters
- recognize differences between TLSv1.3 and other tickets
  * TLSv1.3 tickets are single-use, cache can hold several of them for a peer
  * TLSv1.2 are reused, keep only a single one per peer
- differentiate between ticket BLOB to store (that could be persisted) and object instances
- use put/take/return pattern for cache access
- remember TLS version, ALPN protocol, time received and lifetime of ticket
- auto-expire tickets after their lifetime

Closes #15774

lib/transfer.c

@@ -72,6 +72,7 @@
 #include "url.h"
 #include "getinfo.h"
 #include "vtls/vtls.h"
+#include "vtls/vtls_scache.h"
 #include "vquic/vquic.h"
 #include "select.h"
 #include "multiif.h"
@@ -538,7 +539,7 @@ void Curl_init_CONNECT(struct Curl_easy *data)
  */
 CURLcode Curl_pretransfer(struct Curl_easy *data)
 {
-  CURLcode result;
+  CURLcode result = CURLE_OK;
 
   if(!data->state.url && !data->set.uh) {
     /* we cannot do anything without URL */
@@ -577,12 +578,14 @@ CURLcode Curl_pretransfer(struct Curl_easy *data)
   data->state.httpreq = data->set.method;
   data->state.url = data->set.str[STRING_SET_URL];
 
-  /* Init the SSL session ID cache here. We do it here since we want to do it
-     after the *_setopt() calls (that could specify the size of the cache) but
-     before any transfer takes place. */
-  result = Curl_ssl_initsessions(data, data->set.general_ssl.max_ssl_sessions);
-  if(result)
-    return result;
+#ifdef USE_SSL
+  if(!data->state.ssl_scache) {
+    result = Curl_ssl_scache_create(data->set.general_ssl.max_ssl_sessions,
+                                    2, &data->state.ssl_scache);
+    if(result)
+      return result;
+  }
+#endif
 
   data->state.requests = 0;
   data->state.followlocation = 0; /* reset the location-follow counter */