http,stream: add writableEnded

This is work towards resolving the response.finished confusion and
future deprecation.

Note that implementation-wise, streams have both an ending and ended
state. However, in this case (in order to avoid confusion in user space)
writableEnded is equal to writable.ending. The ending vs ended situation
is internal state required for internal stream logic.

PR-URL: https://github.com/nodejs/node/pull/28934


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>