src: clean up zlib write code

Split the existing `Write()` method into one that takes care
of translating the arguments from JS to C++, and a non-static
method for the actual write operations, as well as some minor
stylistic drive-by fixes.

PR-URL: https://github.com/nodejs/node/pull/23183


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>