Add 12dp padding above the first slice item

-Add an extra padding in adapter for dedicated panels
-Add test cases

Bug: 154181365
Test: manual test
make -j50 RunSettingsRoboTests
"adb shell am start -a android.settings.panel.action.INTERNET_CONNECTIVITY"

Change-Id: I65bc26c23ca5a7f1b433c36ac7ddf1a658793719