lib: merge stream code for http2 streams & net.Socket

Squashed from:

- lib: separate writev responsibilities from writeGeneric
- lib: fix calling of cb twice
- lib: extract streamId out of stream_base to caller
- lib: add symbols instead of methods to hide impl details
- lib: remove unneeded lines
- lib: use Object.assign instead of apply
- lib: rename mixin StreamBase to StreamSharedMethods
- lib: use stream shared funcs as top level instead of
  properties of prototypes
- lib: mv lib/internal/stream_shared_methods.js
  lib/internal/stream_base_commons.js
- lib: add comment for readability
- lib: refactor _writev in Http2Stream
- lib: rephrase comment
- lib: revert usage of const,let for perf reasons

PR-URL: https://github.com/nodejs/node/pull/19527
Refs: https://github.com/nodejs/node/issues/19060


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>