[native] Introduce a JNI network module helper

Summary: This diff makes it possible to expose C++ static methods to java. A first example of such a method will be added in the next diff.

Test Plan: Compile the app - it should not crash.

Reviewers: karol-bisztyga, ashoat, jimpo

Reviewed By: karol-bisztyga, ashoat

Subscribers: jimpo, benschac, ashoat, Adrian, atul

Differential Revision: https://phabricator.ashoat.com/D3132