Allow defining neverallow in packages other than android.

This exposes test func on ValueMatcher and helpers relevant for testing neverallows.

Bug: 153333044
Test: m
Change-Id: Ied07cd33afa537f9d7aa3c33e59f4ac985901a0f
Merged-In: Ied07cd33afa537f9d7aa3c33e59f4ac985901a0f
Exempt-From-Owner-Approval: clean cherry-pick
(cherry picked from commit c5570ac9)