zlib: add script to import zlib 1.2.3 from upstream

CMake has vendored this version for a long time.
Import it using our modern approach.

Utilities/Scripts/update-zlib.bash

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+set -e
+set -x
+shopt -s dotglob
+
+readonly name="zlib"
+readonly ownership="zlib upstream <[email protected]>"
+readonly subtree="Utilities/cmzlib"
+readonly repo="https://github.com/madler/zlib.git"
+readonly tag="v1.2.3"
+readonly shortlog=false
+readonly paths="
+  README
+
+  adler32.c
+  compress.c
+  crc32.c
+  crc32.h
+  deflate.c
+  deflate.h
+  gzio.c
+  inffast.c
+  inffast.h
+  inffixed.h
+  inflate.c
+  inflate.h
+  inftrees.c
+  inftrees.h
+  trees.c
+  trees.h
+  uncompr.c
+  zconf.h
+  zlib.h
+  zutil.c
+  zutil.h
+"
+
+extract_source () {
+    git_archive
+    pushd "${extractdir}/${name}-reduced"
+    echo "* -whitespace" > .gitattributes
+    echo -n "'zlib' general purpose compression library
+version 1.2.3, July 18th, 2005
+
+Copyright " > Copyright.txt
+    sed -n '/^ (C) 1995-/,+19 {s/^  \?//;s/2004/2005/;p}' README >> Copyright.txt
+    popd
+}
+
+. "${BASH_SOURCE%/*}/update-third-party.bash"