Add result metadata to time zone lookup results

This change adds metadata to time zone lookup results which
will enable more sophisticated / better detection logic
in future.

If the device is using multiple sources of time zone
detection then having metadata will enable it to compare
signals and go with the least ambiguous.

The main logic change is that TimeZoneLookupHelper will
return a CountryResult object from lookupByCountry() in
cases when the guessZoneIdByCountry() method that it
replaces returned null. Callers can now check the metadata
for suitability.

android.util.TimeUtils is no longer used for offset lookups,
instead the code goes direct to libcore's TimeZoneFinder
/ CountryTimeZones in all cases.

Included in this commit are some non-functional logging
improvements, comment changes, variable renames and inlining.

Test: atest FrameworksTelephonyTests
Bug: 63743683
Change-Id: I1e67cdb6b564ee8867e4fde361cbb509a3606e6c