doc: fix mistakes in stream doc (object mode)

This patch fixes some trivial documentation mistakes for streams
operating in object mode.

For `unshift()`, `_write()`, `push()` and `_transform()`, the data type
of the `chunk` parameter is extended with `any` and the description
is corrected to take into account that streams can operate in object mode.

PR-URL: https://github.com/nodejs/node/pull/11807


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>