MFC r347244:

Move contrib/zlib to sys/contrib/zlib so that we can use it in kernel.
This is a prerequisite of unifying kernel zlib instances.

Submitted by: Yoshihiro Ota <ota at j.email.ne.jp>
Approved by: re (kib)

Move contrib/zlib to sys/contrib/zlib so that we can use it in kernel.
This is a prerequisite of unifying kernel zlib instances.

Submitted by: Yoshihiro Ota <ota at j.email.ne.jp>
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D20191

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

Copy vendor/libz@250225 to vendor/zlib.

Vendor import of zlib 1.2.4 (trimmed).