Tests for "feature" split APKs.

Adds a new "feature" split APK which contains code, new manifest
components, and its own set of split resources.  Verify that code
and resources from both base and feature coexist, and that they can
interact with each other.

Bug: 16947729
Change-Id: I8cc1a6c3402ce994aacd9c103338393fb3d145f2