Add divider view support for app-pairs

Add divider bar for app-pairs. AppPairLayout and divide policy records
and handles the layout in pair.

Bug: 172704238
Bug: 172704672
Test: manul check the behavior of the splits and divider bar.
Test: AppPairTests, AppPairsPoolTests, AppPairsControllerTests

Change-Id: I688c7001d056fe8dd9a192885e1f9fd5f004dc11