ComposeClock: Add basic clock format for the composable clock

Update the clock text based on the logic in Clock.java's getSmallTime().
This CL add some basic date formatting, with the text updates whenever
there's changes in locale or timezone.

Bug: 390204943
Flag: com.android.systemui.clock_modernization
Test: ClockViewModelTest
Change-Id: I656180fdedbd5e5028f102497d0629c936e90211