http2: order declarations in core.js

Order declarations:

* public modules in alphabetical order
* internal modules in alphabetical order
* process.binding() calls in alphabetical order
* exports in alphabetical order

Backport-PR-URL: https://github.com/nodejs/node/pull/22850
PR-URL: https://github.com/nodejs/node/pull/21689


Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: James M Snell <jasnell@gmail.com>