Add a separate line at the bottom of list area in output switcher

-Bottom divider is not showed when there are more than 7 devices exist in output switcher
-Check panel type in isDividerAllowedBelow()
-Hide the Slice bottom divider of Output switcher panel
-Show divider in panel layout only for output switcher panel

Bug: 159177275
Test: make -j42 RunSettingsRoboTests

Change-Id: I49396a0ee0543b494a2b3d714ec248ebab08e7ba