TLS 1.3: add API to check if a session ticket is still valid

[mpg]

TLS 1.3 clients that want to take full advantage of resumption will have to maintain a pool of the session tickets sent by a particular server. In order to maintain that pool, client need to know if a particular ticket is expired or not. This issue is to add an API supporting that.

Historical note: this issue was split from #6640.