zlib: refactor zlib module

This does several significant things:

1. Refactors the structure of the zlib module, eliminating duplicated code, moving to ES6 classes for simplify inheritance, eliminating some closures and this->self uses. This was done in a way that should preserve API compat (no test changes were required at all for this piece).
2. Makes errors more consistent and improves testing of errors.

Perf impact should be minimal if any.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

zlib