Introduce SessionIdentifierCodec to easily configure encoding/decoding of routing information to/from the session identifier.
Refactor io.undertow.server.session.SessionCookieConfig - extract the SessionConfig implementation into a separate CookieSessionConfig class.
This removes duplicated logic between io.undertow.server.session.SessionCookieConfig and io.undertow.servlet.spec.SessionCookieConfigImpl.
Tidy SessionConfig logic in io.undertow.servlet.spec.ServletContextImpl.initDone().
SecureRandomSessionIdGenerator allows configuration of the session id length, but doesn't actually use the configured value.