zlib one-shot methods

[npaun]

• Reuses ZlibContext from @anonrig's implementation of the stream-based API.
• Sends the entire input buffer at once, and uses only the finishFlush flag, like Node's does.
• Uses GrowableBuffer to collect the output as it's generated. This is basically kj::Vector, but it can be limited to a maximum size and adds some methods to make usage as a buffer more ergonomic.

[npaun]

@jasnell Do we want to respect chunkSize for output even though these are one-shot methods? I think we could theoretically ignore it and pick something larger for performance, but that's not how Node does it.

[anonrig]

I think we should move this function change to a different pull-request.

[npaun]

Normally I'm in favour of splitting PRs into small chunks, however, this time I think the changes are OK to go together, because I'm reusing the input source stuff between zlibsync and crc32sync

[anonrig]

This type is wrong. Technically this supports (null, null), but it is not possible.

Suggested change

	type CompressCallback = (error: Error | null, result: Buffer | null) => void;
	type CompressCallback = ((error: Error, result: null) => void) | ((null, result: Buffer) => void)

[npaun]

Thanks, that's much better.

[npaun]

Hmm, I'm not sure the new type is right either. To me it says "a function that handles errors" OR "a function that handles results". You can't pass in a function that handles both with that type. FWIW, DefinitelyTyped uses a type like the one I had originally.

[npaun]

Addressed the latest round of suggestions; thanks everyone. Please have another look.

[anonrig]

@npaun just fyi: merged commit has WIP: prefix on it.