Update zlib from 1.2.5 to 1.2.11. (mono/mono#15480)

Update zlib from 1.2.5 to 1.2.11. (mono/mono#15480)

Circa 2010 to circa 2017.

Retrieved with apt-get source zlib on WSL Ubuntu 18.04.2 LTS.

This matches Debian or Ubuntu (they differ by one commit, and one of them restores a dummy function for compat).

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* [minizip] Ensure we don't ever accidentally change calling convention

Make sure we always #define ZCALLBACK to empty so we don't change
the calling convention on windows by including a header which defines
'CALLBACK'. This will keep things as cdecl as required by the c#
pinvokes.

* Update zlib readme.

* Update zlib from 1.2.5 to 1.2.11.

* [zlib] Small fix for Visual C++.
see https://github.com/madler/zlib/pull/435/files#diff-0558e84b0c24a83ca790dcb05cd26212R1087
and https://github.com/madler/zlib/pull/435/files#diff-0558e84b0c24a83ca790dcb05cd26212R1104

* Add gzguts.h to Makefiles.

* Add .h files to Visual Studio project files just for GUI purposes.

Commit migrated from https://github.com/mono/mono/commit/431bb95c715abd830a5cfd3e9c37cf79f863cf45