API Enhancement CountryDetector

-Replace CountryListener with a Consumer<Country>
-Add registerCountryDetectorCallback to take an Executor Vs addCountryListener taking Looper
-Add unregisterCountryDetectorCallback to remove Consumer<Country> callback interface
-Adding getSource to return an IntDef
-Expose Country constructor
-Adding alternative API with new naming for getCountryIso
-Refactoring addCountryListener() & removeCountryListener API's

Bug: 252989268, 258197470
CTS-Coverage-Bug: 255511190
Test: manual test && make update-api
Change-Id: I5a2f253a87d1037837bc161a80cb873a6471c229