Introduce Time class to help with migration.

This class will help migrate from android.text.format.Time. Currently,
it has the same API so that no friction is caused in the inital
transition.

Unit tests have been added to ensure future changes don't cause
regressions when transitioning to a more robust Time API.

Bug: 159019762
Test: atest TimeTest
Test: atest CalendarCommonTests
Test: atest CalendarProviderTests
Change-Id: Ic640712cd48f0f4f7abfd8111bdac7d9a430574d