Use consistent NSSL margins across devices

There were some edge cases that were leading to inconsistencies with
the size of the NSSL placeholder and the actual space available. This
was due to differences in how the margins were calculated for the
placeholder.

Test: atest SharedNotificationContainerViewModelTest
Test: manual - use notifications in all orientations and ensure it
matches the legacy location. swipe up/down to make sure animations are
stable
Fixes: 322350556
Fixes: 322554526
Flag: ACONFIG com.android.systemui.keyguard_shade_migration_nssl
DEVELOPMENT
Flag: ACONFIG com.android.systemui.migrate_clocks_to_blueprint
DEVELOPMENT

Change-Id: I99c73a8de19010505cde1a7b41383d304f3d28be