Add a new Insets type for overlapping windows.

- This type will be used in the cases where the app's UI overlaps with some system window or some other WindowContainer hosted by the system.
- Remove the LOCAL_NAVIGATION_BAR 1 & 2 as those are not required and GENERIC_SYSTEM_WINDOW can be used instead of those.

Bug: 232017511
Test: atest WindowContainerTests
Test: atest WindowOrganizerTests
Change-Id: I9d79f39a2a17cb5db4e56439399152a65621c41f