http2: add initial support for originSet

Add new properties to `Http2Session` to identify alpnProtocol,
and indicator about whether the session is TLS or not, and
initial support for origin set (preparinng for `ORIGIN` frame
support and the client-side `Pool` implementation.

The `originSet` is the set of origins for which an `Http2Session`
may be considered authoritative. Per the `ORIGIN` frame spec,
the originSet is only valid on TLS connections, so this is only
exposed when using a `TLSSocket`.

PR-URL: https://github.com/nodejs/node/pull/17935


Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Sebastiaan Deckers <sebdeckers83@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>