Restructure libz, place vendor files in contrib/zlib like other third
party software, this provides more standarized import workflow and
makes future upgrades easier.
The following files are new with this commit:
zconf.h.in
zlib.map
zlib.pc.in
They are not connected to build, but were kept in tree for reference
for future maintenance.
All our local trivial changes were applied to contrib/zlib, and the
contrib/zlib vendor source code is intended to 100% match lib/libz
before this commit.
MFC after: 2 weeks