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/dynbuf.c

@@ -244,6 +244,18 @@ char *Curl_dyn_ptr(const struct dynbuf *s)
   return s->bufr;
 }
 
+char *Curl_dyn_take(struct dynbuf *s, size_t *plen)
+{
+  char *ptr = s->bufr;
+  DEBUGASSERT(s);
+  DEBUGASSERT(s->init == DYNINIT);
+  *plen = s->leng;
+  s->bufr = NULL;
+  s->leng = 0;
+  s->allc = 0;
+  return ptr;
+}
+
 /*
  * Returns an unsigned pointer to the buffer.
  */