Allow the installer of an app to get the app's locales.

Change the api from system to public api so that 3p installers can also use it.

Bug: 210981031
Bug: 193787310
Test: atest FrameworksServicesTests:LocaleManagerServiceTest
Test: atest CtsLocaleManagerTestCases
Change-Id: I98137941749725fbf2fe57d4a33d6abd8f99fffa