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

docs/internals/DYNBUF.md

@@ -132,3 +132,14 @@ CURLcode Curl_dyn_setlen(struct dynbuf *s, size_t len);
 Sets the new shorter length of the buffer in number of bytes. Keeps the
 leftmost set number of bytes, discards the rest. To instead keep the tail part
 of the buffer, see `Curl_dyn_tail()`.
+
+## `Curl_dyn_take`
+
+```c
+char *Curl_dyn_take(struct dynbuf *s, size_t *plen);
+```
+
+Transfers ownership of the internal buffer to the caller. The dynbuf
+resets to its initial state. The returned pointer may be `NULL` if the
+dynbuf never allocated memory. The returned length is the amount of
+data written to the buffer. The actual allocated memory might be larger.