Extract support code for NitzStateMachine tests

Extract utility methods / classes for NitzStateMachine tests;
with two implementations likely to exist for R it makes sense to extract
common code to avoid unnecessary duplication.

Bug: 140712361
Test: atest com.android.internal.telephony.NitzStateMachineImplTest
Change-Id: Id77c2dc57004d4869e234c0432efae7e5d2f5f6a