Add zlib compressor and decompressor (#1766)

Motivation:

v2 should support compression.

Modifications:

- Add a Zlib compressor and decompressor supporting deflate and gzip.
- This is loosely based on the code we had in v1 but refactored to fit
  slightly different requirements.

Result:

Can compress and decompress messages using deflate/gzip

Author: glbrntt

Package.swift

@@ -201,7 +201,8 @@ extension Target {
     dependencies: [
       .grpcCore,
       .nioCore,
-      .nioHTTP2
+      .nioHTTP2,
+      .cgrpcZlib,
     ]
   )