(windows) JNI makefile

Currently, with CMake and modern Debian/testing image in the docker container it is very easy to cross-compile brotli libraries and CLI binary for various target platforms (see https://github.com/google/brotli/wiki/Building-Windows-artifacts).
JNI wrapper library seems to be less fortunate. It requires platform specific pieces and, currently, built only with bazel, which is less than ideal.

So, we are looking for a volunteer who could write a CMake buildfile for that:
* preferably it should depend on the root CMake file
* JNI library should link against static brotli libraries, to be standalone
* for consistency, JNI includes should be taken from the same source as in bazel build
* simple integration test would be a nice bonus