Fix libzip cmake module

libzip installs `zipconf.h` in `$prefix/$libdir/libzip/include/`. Some
systems (e.g. archlinux) symlink this file under `$prefix/$libdir/include`
for compatibility reasons, but cmake fails on systems that do not (e.g.
flatpak). Since libzip supports pkg-config, we can just query pkg-config
which gives us the proper path we are looking for. While at it, use
pkg-config also to get the library version (replacing our custom parsing code
which does not work) and follow general cmake best-practices.

This breaks the Applications dependency freeze, but it's an important
fix so it should go in.

Differential Revision: D5101