Add unit tests for End-aligning short shelf on split shade when

minimalism enabled

Add unit tests for aligning the short shelf to the end for split shade
on lock screen when the notification minimalism is enabled.

Bug: 357643925
Flag: com.android.server.notification.notification_minimalism
Test: atest NotificationShelfTest
Change-Id: I5935fdb00409be15633bf583b19249586ee2ecd0