zlib: magical async/sync depending on callback

[mscdex]

9b37b83a20 adds synchronous versions of the various zlib functions. However, it's implemented such that the synchronous versions are automatically used if a callback is not supplied.

I think that the synchronous code should follow what the fs module does and 'Sync' should be appended to the names of separate functions that do the synchronous work. To me, appending 'Sync' makes it much easier to reason about code by being more explicit about the behavior of the function.

[trevnorris]

Fixed by 2315703