Move time zone lookup logic

Move time zone lookup logic into a separate TimeZoneLookupHelper which
can be independently tested and improved. Tests for all methods there
have been added / migrated & improved.

This also allows the lookup behavior to be mocked for NitzStateMachineTest
which has been adjusted accordingly. An additional test has been added
to demonstrate.

TimeStampedValue has been moved to a top-level class under util so
it can be used more widely and from tests.

Test: atest FrameworksTelephonyTests
Bug: 63743683
Change-Id: I2ff15b1355d5ba690198c5943bcb0faed17d8210