http2: allow fully synchronous `_final()`

HTTP/2 streams do not use the fact that the native
`StreamBase::Shutdown()` is asynchronous by default and
always finish synchronously.

Adding a status code for this scenario allows skipping an
expensive `MakeCallback()` C++/JS boundary crossing.

PR-URL: https://github.com/nodejs/node/pull/25609


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>