Add lookupTimeZoneIdsByCountry

Add lookupTimeZoneIdsByCountry for use by settings
code. The settings code doesn't need full TimeZone
objects.

Bug: 36971201
Test: run cts -m CtsLibcoreTestCases -t libcore.util.TimeZoneFinderTest
Change-Id: Ic85d1b7e63856078fc10ad9eaeed1aff52fc9171
Merged-In: Ic85d1b7e63856078fc10ad9eaeed1aff52fc9171
(cherry picked from commit e065f8ab)